Hydrophilic surfaces carrying temporary protective covers

ABSTRACT

A substrate carrying a temporary protective cover and related methods of producing and processing substrates are described. In one embodiment, a substrate bears a hydrophilic coating carrying a temporary protective cover that protects the hydrophilic coating against contamination but that can readily be readily removed from the hydrophilic coating by washing with a given washing fluid.

RELATED APPLICATIONS

This is a Divisional of U.S. application Ser. No. 10/009,284, filed Oct.11, 2002, now U.S. Pat. No. 6,902,813 which claims priority to a 371 ofPCT/US01/28728, filed Sep. 11, 2001, all of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention provides a temporary protective cover forsubstrates, such as glass and the like. More particularly, the inventionprovides a temporary cover that can be applied over a substrate surfaceto protect such surface from contamination.

BACKGROUND OF THE INVENTION

It can be difficult to prevent newly manufactured glass and othersubstrates from accumulating contaminants from the manufacturingenvironment. Manufacturing environments commonly contain organics andother residues that can contaminate the substrates being produced. Forexample, various solvents, curing products, and sealants used inmanufacturing glass and glass products produce residues that canaccumulate on the glass being produced. The atmosphere in themanufacturing facility may also contain vapors that condense on, orotherwise contaminate, the manufactured glass. For example, silicone iscommonly used as a sealant in the manufacture of insulating glass units(IG units). Newly deposited silicone may outgas for significant periodsof time. As a consequence, glass may accumulate silicone residue aftersimply being exposed to an ambient manufacturing environment. In fact,it has been discovered that this type of silicone contamination is verydifficult to prevent. Unfortunately, silicone contamination can also beextremely difficult to remove.

Contamination can occur in several other ways during manufacturingprocesses. For example, glass sheets are commonly conveyed acrossrollers as they are coated. During conveyance, the bottom surface of theglass is in supportive contact with the rollers, which can leave minorimpurities or traces of contact. While these imperfections tend to bevery slight, they are unwanted and should be avoided if possible.Handling equipment used in producing glass products can also leave markson the glass. For example, vacuumized suction cups are commonly used tohandle glass sheets. This has been found to leave suction cup marks onthe glass, at least in some instances. Stickers and other markings mayalso be applied during glass production. These stickers and markingstend to be easily removed. However, it can be difficult to assure theywill have no permanent effect on the glass surfaces from which they areremoved.

Glass sheets and other substrates are subjected to other contaminationsources after leaving the manufacturing facility. For example, glassproducts may be exposed to a variety of storage and transportenvironments before reaching their final destination. Like manufacturingfacilities, storage and transport environments may contain residues andvapors that can accumulate on and contaminate the products therein. Forexample, IG units and other products found in storage and transportenvironments may contain silicone sealants and other materials that canoutgas for substantial periods of time. Of course, many of theseenvironments are outside the manufacturer's control. Thus, while amanufacturer may attempt to control the environment within its ownmanufacturing and storage facilities, it would be very difficult toregulate each of the environments to which glass may be exposed prior todelivery to the ultimate consumer.

Contamination can also occur when glass products are installed orfinished. The contamination that is perhaps most familiar to newhomeowners occurs when window frames are painted and some of the paintunintentionally ends up on a window pane. While installers and painterscan take steps to temporarily mask the surfaces of nearby glass (e.g.,by applying “masking tape”), it can be difficult to mask the entiresurface of the glass. Thus, any unmasked surface areas will still bevulnerable to unintentional spills and drips. Moreover, to the extentthese tapes are applied with adhesive, it can be difficult to assurethat no adhesive residue is left on the glass following removal.

Contamination sources like these can be particularly problematic when itis desired to produce glass with specific surface properties. Forexample, it may be desirable to produce glass bearing a hydrophiliccoating. Hydrophilic coatings have an affinity for water and tend tocause water applied thereto to sheet. As described in U.S. patentapplication Ser. Nos. 09/868,542, 09/868,543, 09/599,301, and09/572,766, the entire contents of each of which are incorporated hereinby reference, hydrophilic coatings may be particularly advantageous whenused on architectural glass and other substrates. For example, thesecoatings are believed to resist formation of water stains, therebypromoting a longer lasting clean appearance.

The production of glass and other substrates having hydrophilic surfaceproperties can be surprisingly challenging. For example, contaminationsources of the likes discussed above can make it exceedingly difficultto manufacture, transport, install, and finish substrates bearinghydrophilic coatings that retain the desired hydrophilic properties ofthe pristine coating. For example, the accumulation of silicones on anotherwise hydrophilic surface can cause that surface to become morehydrophobic than is desired. As noted above, silicone contamination hasbeen found to surprisingly difficult to prevent.

The most obvious solution to this problem would be to simply remove thesurface contamination, such as by washing or otherwise cleaning thecontaminated surface. For example, various polishing and etching agentshave been used to remove paint contamination from window panes.Technicians have even been known to use razorblades to scrape paint andthe like off glass. Unfortunately, these aggressive treatments mayactually remove some of the glass, leaving dull or scratched areas. Evenwith aggressive cleaning methods, silicone contamination can bevirtually impossible to remove. For example, when glass bearing ahydrophilic coating becomes contaminated with silicone, subsequentcleaning may appear to remove the silicone contamination, yet thehydrophilic properties of the coating may not be fully restored.

Another solution would be to temporarily protect the hydrophilic coatingon a substrate during periods of potential contamination. In the past,attempts have been made to protect glass with removable papers andplastics. Typically, these papers and plastics are removed bymechanically peeling them from the substrate. Reference is made to U.S.Pat. No. 1,256,818 (Nile), U.S. Pat. No. 5,107643 (Swensen), and U.S.Pat. Nos. 5,599,422 and 5,866,260 (both to Adams, Jr. et al.), theentire contents of each of which are incorporated herein by reference.

Unfortunately, protective papers and plastics have a number ofdisadvantages. For example, they are commonly applied using adhesives.These adhesives may react with glass, rendering them difficult to removeand possibly altering the surface properties of the glass. This may beparticularly likely in cases where the glass is masked for long periodsof time or where the masked glass is exposed to high temperatures orsubstantial radiation (e.g., sunlight). Components of certain papers andplastics, such as those containing silicone, may also react with glassin these ways. Non-adhesive applications, such as those relying onstatic cling, would seem possible. However, papers and plastics appliedin this manner may be less secure than desired, perhaps even falling offduring handling. Further, when protective papers and plastics areremoved, they generate additional waste that must be discarded orrecycled, thus creating additional labor and expense.

Attempts have also been made to temporarily protect glass by applyingliquid coating compositions through a variety of wet depositionprocesses (e.g., painting, dipping, or spraying). While the resultingcoatings vary in composition, many of them are polymeric materials thatare removed by peeling or by washing with water. Reference is made toU.S. Pat. No. 5,453,459 (Roberts), U.S. Pat. Nos. 5,866,199 and6,124,044 (both to Swidler), and International (PCT) Publication NumbersWO 00/50354 (McDonald) and WO 01/02496 (Medwick et al.). The Medwick etal. reference also discloses a sputtered carbon-containing coating thatcan be used to temporarily protect glass. The coating is said to beremovable by combustion. For example, Medwick et al. expressly indicatethat their coating would be oxidized and removed during tempering.Unfortunately, all of these approaches are less than ideal.

The limitations of these approaches become more apparent when oneconsiders the full scope of processing that a typical window endures.Glass sheets can be formed by a number of processes, perhaps the mostcommon of which is the float glass process. In this process, the basicelements of glass are combined and heated in a furnace to temperatureson the order of 2900° F., whereby the glass becomes molten. A ribbon ofthis glass is then floated atop a molten tin bath where it begins tocool and is machined to a desired width and thickness. The glass is thencut into smaller sheets.

Glass sheets can be coated with a variety of different coatings using avariety of different coating methods. Sputter deposition is a commonmethod for applying coatings to large area substrates, such as glass forarchitectural applications. When glass sheets are coated by sputterdeposition, the sheets are conveyed into a sputtering chamber.Typically, the glass is conveyed through a series of connectedsputtering chambers (i.e., a sputtering line), each containing acontrolled sputtering atmosphere. As the glass sheets are conveyedthrough the sputtering line, the desired coatings (e.g., a hydrophiliccoating) are sputtered onto the glass. At the outlet of the sputteringline, the glass is removed from the controlled sputtering atmosphere andis exposed to the ambient glass processing atmosphere. At this point,the coated glass may begin to accumulate contamination from theenvironment.

Thus, coated glass is typically vulnerable to becoming contaminated onceit is removed from a controlled coating environment. As a consequence,it would be desirable to apply temporary protection to a coatedsubstrate at the same time the substrate is coated. For example, itwould be desirable to apply a temporary protective cover oversputter-coated glass before removing the glass from the sputtering line.

It would likely be difficult to apply papers, plastics, or liquidcoating compositions inside a sputtering chamber. For example, theelevated substrate temperatures that occur during sputtering would tendto make application challenging. During sputtering, glass commonlyreaches temperatures on the order of 100-200° C., and may reach evenhigher temperatures for certain processes. These temperatures would beabove the softening points of many plastics and many adhesives used toapply papers or plastics. Further, conventional sputtering chambers arenot configured for wet deposition processes. Thus, it would likely beimpractical, if not impossible, to apply any of these protectivematerials in a sputtering chamber. Even if it were feasible to applythese protective materials in a sputtering chamber, these materials maynot withstand the processing to which many substrates are subjectedafter they are coated.

Once glass is removed from a coating atmosphere (e.g., a sputteringchamber), it is typically covered with a so-called “separator”. Typicalseparator comprises a protective powder (e.g., adipic acid powder),which protects the glass against moisture corrosion. The powder commonlycontains small beads (e.g., nylon beads), which separate the glasssheets when they are stacked against one another. These beads preventthe surfaces of adjacent sheets in a stack from coming into contact withone another, thereby minimizing abrasion and other damage.

As noted above, glass sheets are sometimes assembled into IG units. Asone of the first steps in this process, the separator is typicallywashed from the glass sheets. This is conventionally accomplished bypassing the glass sheets through industrial glass washing machines.Industrial glass washers typically apply water, which may be hot, andoptional detergents to the glass. Most protective papers and plasticswould not be expected to survive being run through an industrial glasswasher. Moreover, deterioration of these materials could create aterrible mess inside a washing machine, perhaps clogging the machine andcomplicating its maintenance. Further, many protective materials thatare applied in liquid form are water soluble. Thus, it would bedesirable to provide a temporary protective cover that is durable toindustrial washing.

Coated glass may also be subjected to various elevated temperatureprocesses, such as heat tempering or bending. During tempering, forexample, glass is commonly heated to temperatures on the order of about600° C. (1112° F.) for substantial periods of time (e.g., hours).Unfortunately, most protective papers, plastics, and polymeric materialswould be burned-off, or at least significantly deteriorated, duringelevated temperature processing. Likewise, the carbon-containingprotective coating described in the Medwick et al. reference is said tobe burned-off during tempering. Since tempered glass may be exposed tocontamination sources after tempering (e.g., during subsequent storage,transport, installation, and finishing), it would be advantageous toprovide a temporary protective cover that is durable to tempering.

It would be desirable to provide temporary protective covers that can beapplied to coated substrates as part of the coating process. Forexample, it would be advantageous to provide temporary covers that canbe applied to sputter-coated glass in the controlled sputteringenvironment. It would be particularly desirable to provide temporarycovers that are sufficiently durable to withstand the full scope ofprocessing that glass and other substrates typically endure. Forexample, it would be advantageous to provide temporary covers that aredurable to industrial glass washing and the like. It would be especiallydesirable to provide a temporary cover that is durable to elevatedtemperature processing (e.g., heat tempering and bending). At the sametime, it would be desirable to provide a temporary cover that can bereadily removed after installation or finishing, or at any stage when itis desired to expose the underlying surface.

SUMMARY OF THE INVENTION

It has now been found that a hydrophilic coating can be protectedagainst contamination by providing on the coating a temporary protectivecover that breaks down and can be removed by washing the cover with awashing fluid that does not break down the coating. The cover protectsthe hydrophilic coating from becoming contaminated with e.g., siliconeused in the window industry. Once the cover is no longer desired, it canbe washed readily from the hydrophilic coating with the washing fluid(e.g., which may be an aqueous acidic or alkaline solution, for example,vinegar). By removing the protective cover, which may itself becomecontaminated with silicones (and hence rendered hydrophobic), the clean,pristine surface of the hydrophilic coating is exposed.

In one embodiment, the invention provides a substrate having an exteriorsurface bearing a hydrophilic coating that is resistant to attack by aweak acid or a weak base. The hydrophilic coating carries a temporaryprotective cover that is stable in the presence of water, but breaksdown in the presence of a weak acid or a weak base.

In another embodiment, the invention provides an insulating glass unitcomprising spaced-apart panes with confronting interior surfaces thatbound a between-pane space. At least one of the panes has an exteriorsurface bearing a hydrophilic coating that is durable to a given washingfluid. The hydrophilic coating carries a temporary protective covercomprising a sputtered film that protects the hydrophilic coatingagainst contamination, but that can readily be removed from thehydrophilic coating by washing with said washing fluid.

In still another embodiment, the invention provides a substrate bearinga hydrophilic coating comprising silicon dioxide formed directly uponthe substrate. The hydrophilic coating is durable to a given washingfluid. Further, the hydrophilic coating carries a temporary protectivecover comprising a sputtered film that protects the hydrophilic coatingagainst contamination, but that can readily be removed from thehydrophilic coating by washing with said washing fluid.

In yet another embodiment, the invention provides a method of producingsubstrates. The method comprises providing a substrate with generallyopposed interior and exterior surfaces. A hydrophilic coating is formedupon the exterior surface of the substrate. The hydrophilic coatingcomprises material that is resistant to attack by a weak acid or a weakbase. A temporary protective cover is formed over the hydrophiliccoating. The cover comprises material that is stable in the presence ofwater but breaks down in the presence of a weak acid or a weak base.

A further embodiment of the invention provides a method of processingsubstrates. The method comprises providing a substrate having anexterior surface bearing a hydrophilic coating that is durable to agiven washing fluid. The hydrophilic coating carries a temporaryprotective cover comprising a sputtered film that protects thehydrophilic coating against contamination but that can readily beremoved from the hydrophilic coating by washing with the washing fluid.The covered exterior surface of the substrate is washed with the washingfluid to remove at least a portion of the cover, thereby exposing atleast a portion of the hydrophilic coating.

In another embodiment, the invention provides a substrate, such as aglass sheet, having a hydrophilic surface that is durable in that it ishighly resistant to a desired washing fluid. The hydrophilic surface canbe the surface of the substrate, or it can be a surface that resultsfrom depositing a hydrophilic coating onto the substrate. Hydrophilicsurfaces and coatings that are not sufficiently durable to withstandconventional washing procedures, or the application of the desiredwashing fluid, are less desirable for use in the present embodiment.Directly upon the hydrophilic surface is deposited a temporaryprotective cover of a type and of a thickness that protects thehydrophilic surface from contamination, as by silicone rubber compounds,but that yet is of a nature enabling it to be readily broken down andwashed from the hydrophilic surface through use of the desired washingsolution, preferably an aqueous solution, and most preferably a solutionthat is at least slightly basic or slightly acidic in nature.

In still another embodiment, the invention provides a method that can beused in the manufacture and installation of windows. The method involvesproviding a window with a hydrophilic surface that is durable to aparticular washing fluid, coating upon the hydrophilic surface aprotective cover to protect the hydrophilic surface from contamination,and eventually washing the protective cover from the hydrophilic surfacewith a washing fluid capable of breaking up the protective cover but notharming the hydrophilic surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a is a schematic cross-sectional view of a substrate having acoated surface carrying a temporary cover in accordance with oneembodiment of the present invention;

FIG. 2 is a schematic cross-sectional view of a substrate having twocoated surfaces one of which carries a temporary cover in accordancewith another embodiment of the invention;

FIG. 3 is a schematic cross-sectional illustration of a multiple-paneinsulating glass unit wherein a coated surface of one of the panescarries a temporary cover in accordance with still another embodiment ofthe invention;

FIG. 4 is a is a schematic cross-sectional view of a substrate having acoated surface carrying a temporary cover in accordance with a furtherembodiment of the invention;

FIG. 5 is a schematic cross-sectional view of a substrate having twocoated surfaces each carrying a temporary cover in accordance withanother embodiment of the invention;

FIG. 6 is a schematic illustration of a dual-direction sputteringchamber for use in accordance with one method of the invention; and

FIG. 7 is a schematic illustration of a multiple-zone dual-directionsputtering chamber for use in accordance with another method of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description is to be read with reference to thedrawings, in which like elements in different drawings have been givenlike reference numerals. The drawings, which are not necessarily toscale, depict selected embodiments and are not intended to limit thescope of the invention. Examples of constructions, materials,dimensions, and manufacturing processes are provided for selectedelements. All other elements employ that which is known to those ofskill in the art of the invention. Skilled artisans will recognize thatthe examples provided herein have many suitable alternatives that can beutilized, and which fall within the scope of the invention.

FIG. 1 illustrates a substrate 10 having an exterior surface 12 thatbears a hydrophilic coating 20. The hydrophilic coating 20 carries atemporary protective cover 90 in accordance with the present invention.The exterior surface of the substrate is designated by the referencenumeral 12, and the interior surface is designated by the referencenumeral 14. The designations herein of “interior” and “exterior”surfaces are somewhat arbitrary. For example, neither the “exterior”surface nor the “interior” must necessarily be exposed to an outdoorenvironment, unless such requirement is explicitly stated.

Substrates suitable for use in connection with the present inventioninclude the particular substrate class comprising generally flat,sheet-like substrates. A substrate of this nature typically has twogenerally-opposed major surfaces 12, 14. For example, this class ofsubstrates includes sheets of glass and the like. In fact, temporaryprotective covers of the invention can be used quite advantageously toprotect glass substrates from becoming contaminated. One type of glasssubstrate that is commonly used in manufacturing glass articles (e.g.,insulating glass units) is generally referred to as soda-lime glass.Other types of glass that may be suitable include those generallyreferred to as alkali-lime-silicon dioxide glass, boro-silicon dioxideteglass, alumnino-silicon dioxidete glass, boro-alumino silicon dioxideteglass, phosphate glass, and fused silicon dioxide. It is noted that thesubstrate 10 is not required to be transparent. For example, opaquesubstrates may be useful in some cases. However, it is anticipated thatfor most applications, the substrate will comprise a transparent ortranslucent material, such as glass or clear plastic.

The temporary protective covers 90 of the present invention areparticularly useful for protecting substrates that have hydrophilicsurface properties. As noted above, glass sheets that initially havehydrophilic surface properties may become contaminated at various stagesof production. For example, it has been discovered to be surprisinglydifficult to produce architectural glass bearing hydrophilic coatingswithout materials like silicone contaminating the coated glass.Unfortunately, silicone and other contaminants can cause otherwisehydrophilic surfaces to become undesirably hydrophobic. However, bytemporarily protecting newly manufactured hydrophilic coatings with thepresent covers 90, a manufacturer can be more assured that the ultimateconsumer will enjoy the intended hydrophilic properties of thesecoatings.

FIG. 1 illustrates a preferred embodiment wherein there is provided asubstrate 10 bearing a hydrophilic coating 20. In the illustratedembodiment, the hydrophilic coating 20 is formed directly upon theexterior surface 12 of the substrate 10, although this is by no means arequirement. As described below, the hydrophilic coating 20 mayalternatively be formed upon one or more previously deposited films onthe substrate 10. The hydrophilic coating 20 carries a temporaryprotective cover 90 in accordance with the present invention. Theillustrated cover 90 is formed directly upon the hydrophilic coating 20,although this is not required. In the illustrated embodiment, theinterior surface 14 of the substrate 10 does not carry a protectivecover. However, one could be provided if so desired.

The present temporary covers 90 can be used advantageously to preventcontamination of any type of hydrophilic coating or surface. While FIG.1 shows a substrate 10 bearing a discrete hydrophilic coating 20, thisis not a requirement of the invention. For example, the surface of thesubstrate 10 may itself be hydrophilic. This may be an inherent propertyof the substrate material, or it may be a result of a particular surfacetreatment performed upon the substrate 10. The term “hydrophilic” isused herein to refer to any coating or surface that tends to cause waterapplied thereto to form a sheet, rather than to bead up. For example,hydrophilic coatings and surfaces would be expected to have a contactangle with water, prior to being at all contaminated, of less than about25 degrees.

The present covers 90 can be used in conjunction with any desired typeof hydrophilic coating. As described below, in one particularlypreferred embodiment, the hydrophilic coating 20 is an oxide. However,this is by no means a requirement, as a variety of suitable materialscould be used. Preferably, the hydrophilic coating 20 is formed ofmaterial that has a contact angle with water of less than about 25degrees before the coating 20 is exposed to any environmentalcontamination and after the protective cover 90 has been removed.

Desirably, the hydrophilic coating 20 has good mechanical durability.For example, this coating 20 preferably has sufficient mechanicaldurability to withstand the rigors of common window washing techniqueswithout becoming unacceptably scratched or otherwise damaged. It is alsodesirable for the hydrophilic coating 20 to be resistant to attack by(i.e., stable in the presence of) a washing fluid that is at leastslightly acidic or basic. Preferably, this coating 20 is resistant toattack by a mild acid or a mild base. Optimally, this coating 20 isentirely unaffected by contact with mild acids and mild bases.

As the hydrophilic coating 20 will be exposed following removal of theprotective cover 90, it is desirable that it 20 be sufficiently durableto withstand the environment to which it will be exposed. In some cases,the hydrophilic coating 20 will be destined for exposure to an outdoorenvironment. In these cases, the hydrophilic coating 20 is preferablydurable to (i.e., adapted to withstand) prolonged exposure to external(i.e., outdoor) weather conditions, such as periodic contact with rain(i.e., water which may be slightly acidic or basic). Thus, thehydrophilic coating 20 is desirably both physically and chemicallydurable.

In a particularly preferred embodiment, the hydrophilic coating 20 is acertain preferred water-sheeting coating. The preferred water-sheetingcoating is described in detail in U.S. patent application Ser. Nos.09/868,542 and 09/599,301, the entire teachings of each of which areincorporated herein by reference. The coating is comprised of silicondioxide, which advantageously is substantially non-porous. As describedbelow, the exterior face of the silicon dioxide may have an irregularsurface. Accordingly, attributing a specific thickness to such a coatingmay be somewhat difficult and inaccurate. However, a median thickness ofbetween about 15 angstroms and about 350 angstroms is believed to bepreferred, with a median thickness of between about 15 angstroms andabout 150 angstroms being more preferred. The major benefit of thiscoating 20 at the least cost is believed to be evidenced at a medianthickness range of between about 20 angstroms and about 120 angstroms.

The preferred water-sheeting coating 20 is preferably applied bysputtering. Sputtering techniques and equipment are well known in theart. For example, magnetron sputtering chambers and related equipmentare commercially available from a variety of sources (e.g., Leybold andBOC Coating Technology). Useful magnetron sputtering techniques andequipment are also disclosed in U.S. Pat. No. 4,166,018 (Chapin) andU.S. Pat. No. 5,645,699 (Sieck), the entire teachings of each of whichare incorporated herein by reference.

Generally speaking, magnetron sputtering involves providing at least onetarget formed of material to be deposited upon a substrate 10. In thisprocess, a clean substrate (e.g., glass) is placed in a coating chamberwhich is evacuated, preferably to less than 10⁻⁴ torr, more preferablyless than 2×10⁻⁵ torr. The target is provided with a negative charge anda relatively positively charged anode is positioned adjacent the target.By introducing a relatively small amount of a desired gas into thechamber adjacent the target, a plasma of that gas can be established.Particles (e.g., ions) in the plasma collide with the target, knockingtarget material off the target and sputtering it onto the substrate. Tofacilitate this process, it is known to position magnets behind thetarget to shape and focus the plasma about a sputtering surface of thetarget.

Conventional magnetron sputtering techniques and equipment can be usedto apply the preferred water-sheeting coating 20. For example, thiscoating 20 can be deposited by sputtering silicon dioxide targets in aninert atmosphere. However, it can be extremely difficult to reliablysputter silicon dioxide targets. This is because targets serve ascathodes in conventional magnetron sputtering processes and becausesilicon dioxide is a poor conductor. As a result, it is preferred thatthe water-sheeting coating 20 be deposited using targets comprisingmetallic silicon rather than silicon dioxide. The material actuallydeposited on the substrate can be converted to silicon dioxide byemploying a sputtering atmosphere that includes oxygen.

The silicon targets are preferably not formed of pure silicon. Rather,the targets more preferably comprise a compound of silicon and aluminum.Pure silicon targets are difficult to sputter in a consistent,controlled fashion because silicon is a semiconductor. As a consequence,some of the silicon dioxide (which is non-conductive) that is emittedwhen sputtering pure silicon targets is re-deposited on the targetsurfaces, as well as on the anodes and surrounding shields in thesputtering chamber. This can affect the flow of current, which in turnmay cause arcing if sputtering is continued. Thus, to reduce arcing, itis preferred that the targets include about 5% aluminum or the like.Targets of this nature are available from well known commercialsuppliers, such as Bekaert VDS nv, which is located in Deinze, Belgium.

The atmosphere in the sputtering chamber can be varied to achieve anoptimized sputtering rate. An oxidizing sputtering atmosphere ispreferably employed in cases where silicon or silicon-aluminum targetsare used. Of course, the sputtering atmosphere need not be pure oxygenin these cases. To the contrary, a mixture comprising oxygen and inertgas (e.g., argon) will tend to enhance the sputtering rate. For example,it is believed that a sputtering atmosphere comprising oxygen and up toabout 40% argon (preferably 0-20% argon) maintained at about 3×10⁻³ mbarwill suffice. The power applied to each target is preferably optimizedto reduce arcing yet maximize sputtering rate.

One manufacturing arrangement that has given good results employs threerotary sputtering targets of silicon doped with about 5% aluminum (i.e.,about 95% silicon and about 5% aluminum) with a power of about 42 kWapplied to each target. The atmosphere in the sputtering chamber maycomprise 100% O₂ at a pressure of about 2.5-4.5 mTorr. Alternatively, anatmosphere comprising about 80% oxygen and about 20% argon maintained atabout 3×10⁻³ mbar can be used. The substrate 10 can be moved past thesputtering targets at about 100-500 inches per minute. Of course, theprecise operating conditions (e.g., substrate speed, power, plasmacomposition, target composition, etc.) under which the preferredwater-sheeting coating 20 is applied can be varied as desired tooptimize deposition of this coating 20 at different thicknesses. Giventhe present teaching as a guide, one of ordinary skill in the art wouldbe able to readily select and vary suitable operating conditions toapply the preferred water-sheeting coating 20 at different thicknesses.

Thus, in a particularly preferred method of the invention, the preferredwater-sheeting coating 20 is deposited by moving a substrate 10 beneatha plurality of silicon-aluminum targets while sputtering the targets inan oxidizing atmosphere. If so desired, this atmosphere may consist onlyof oxygen and inert gas. While this is by no means a requirement,sputtering atmospheres of this nature have given good results. A coating20 deposited by such a method would be expected to consist only ofsilicon dioxide and perhaps a small amount of aluminum (or another metalprovided in the targets to enhance conductivity), at least wheninitially deposited.

It has been found that sputter depositing silicon dioxide on a substratein accordance with the present disclosure yields a coating with asignificantly more irregular surface than uncoated glass surfaces.Photomicrographs of the preferred water-sheeting coating 20 (which areillustrated in the above-incorporated U.S. patent application Ser. No.09/868,542) illustrate a surface characterized by a plurality ofspaced-apart fairly sharp, distinct peaks rising significantly above therest of the surface. While it is acknowledged that these micrographs maybe atypical of the overall surfaces of such coatings, they do appear tosuggest that the surface of the present water-sheeting coating 20 isirregular and substantially non-porous.

The behavior of a sheet of glass bearing the preferred water-sheetingcoating 20 is visibly different from that of a similar sheet of glassnot bearing such a coating. A glass surface bearing the preferredwater-sheeting coating 20 tends to sheet water more readily and isnoticeably easier to clean to the point where no visible streaks ordefects remain than is a comparable sheet of uncoated glass under thesame conditions.

To provide an accurate comparison of the preferred water-sheetingcoating 20 to a directly comparable sheet of glass not bearing thecoating, a comparative sample was prepared. A plain, untreated pane ofglass was thoroughly cleaned and laid horizontally on a set of rollers.A small, square piece of glass was laid on the upper surface of the paneof glass to serve as a template covering part of the surface of thepane. The pane and overlying template were passed into a magnetronsputtering chamber and a coating of about 35 angstroms of SiO₂ wasdeposited. The template was then removed, leaving a pane of glass withthe preferred water-sheeting coating 20 over most of its surface, buthaving an uncoated area that was beneath the template during sputtering.The opposite side of the glass, i.e., the side of the glass facing awayfrom the side provided with the SiO₂ coating, was coated with a lowemissivity, infrared-reflective film stack having two silver layersspaced apart from one another and from the glass using a plurality ofdielectric layers.

The partially coated surface of the glass pane was visibly inspected.When completely clean, the boundaries of the uncoated area that wasbeneath the template during sputtering were essentially undetectable tothe unaided eye, indicating that the water-sheeting coating had aminimal impact on the basic optical properties of the glass. A finespray of atomized water droplets was sprayed on the surface using asimple, hand-operated spray bottle of the type conventionally used tospray household cleaning products. Once the spray was applied, theboundaries of the uncoated area were readily visible. The water on thearea bearing the coating sheeted to an apparently uniform film of water,but the area without the coating had a less uniform appearance.

A conventional cleaning solution commercially available under thetrademark Windex® was sprayed on the surface of the glass pane and thesurface was wiped with a paper towel until the area bearing thewater-sheeting coating appeared dry and no longer showed any visiblestreaks. At this time, the uncoated area still had visible streaks ofmoisture. While these visible streaks on the uncoated area eventuallydried without leaving any substantial residual streaking on the glass,it is believed that the average person would tend to continue to wipethis area until all visible streaks disappeared, meaning that the personwould expend less time and effort cleaning a glass article bearing thewater-sheeting coating 20 than a glass article without such a coating.These results indicate that the preferred water-sheeting coating 20makes glass coated therewith significantly easier to clean than uncoatedglass.

While the hydrophilic coating 20 can be quite advantageously formed ofsputtered silicon dioxide, as just described, this is by no means arequirement. Rather, any desired hydrophilic coating can be used. Forexample, other useful hydrophilic coatings are described in U.S. patentapplication Ser. No. 09/576,766, the entire teachings of which areincorporated herein by reference. Further, those skilled in the art maywish to employ other types of hydrophilic coatings, all of which wouldderive particular benefit from the present covers 90.

The temporary protective cover 90 desirably comprises a film that isquite thin (e.g., on the order of 2500 angstroms or less). In fact, theprotective cover 90 preferably has a total thickness of less than about100 angstroms. Thicknesses in this range are preferable as theyfacilitate complete, uniform removal of the cover 90 upon washing thecovered surface of the substrate with the desired washing fluid. Theterms “covered surface” and “covered substrate” are used herein to referrespectively to a surface and a substrate at a time when the cover 90 isin place (i.e., before the cover has been removed).

Covers 90 having a thickness of more than 100 angstroms may bebeneficial for certain applications. However, it has been discoveredthat such covers are not as easily washed away. For example, unusuallythick covers have been found to require longer washing times. Moreover,one must be careful to completely and uniformly remove such coversduring the washing process. Further, when an unusually thick cover isused, washing is more likely to leave an irregular surface, retainingunremoved material from the cover 90. These irregular surfaces have beenfound to possess an undesirable wavy or blotchy appearance. Moreover, ithas been discovered that it is difficult to determine when the entirecover 90 has been washed away if an unusually thick cover 90 is used.

It should be noted, however, that the thickness of the cover 90 could beincreased beyond the preferred range mentioned above. For example, it isnot a requirement for the temporary cover 90 to have an opticallyinsignificant thickness. The present covers 90 are intended to beremoved. Thus, they can be deposited at an optically significantthickness. In many cases, though, it will be preferable to employ acover 90 that is optically insignificant. For example, it may bedesirable to manufacture glass sheets that carry temporary protectivecovers 90 on both major surfaces (i.e., the interior surface and theexterior surface). When glass sheets are incorporated into multiple-paneIG units, the inner surfaces of the panes will be exposed to theprotected space between the panes (i.e., the “between-pane space”),while the outer surfaces will be exposed to an environment external tothe IG unit (i.e., they will not be encased within the between-panespace). Thus, it may be desirable to have the flexibility to leave theprotective covers 90 on surfaces that are destined to be encased withinthe between-pane space of an IG unit. In these cases, the covers 90 thatwill be left on the glass are, of course, preferably opticallyinsignificant, so as not to change the optical properties of the IGunit. Unless the encased surfaces of an IG unit become visiblycontaminated, removing the covers 90 from these surfaces may beunnecessary.

In most cases, it is anticipated that the preferred thickness range forthe protective cover 90 will be less than about 100 angstroms. As notedabove, the present covers 90 are preferably removable upon being washedwith a weak acid or a weak base. Therefore, no particular maximumthickness is required. However, the covers 90 should be thick enough toprovide protection against contamination from silicones and otherenvironmental organics and residues. That is, the cover 90 is preferablythick enough and dense enough to prevent such contamination frompermeating the cover 90 and contaminating the underlying hydrophiliccoating 20. It is anticipated that a protective cover 90 formed inaccordance with the present teaching and having a thickness as small asabout 5-10 angstroms would be suitable to serve this purpose. However,the major benefit of the present cover 90 in terms of protection againstcontamination and predictably uniform removability is believed to existat a range of between about 25 angstroms and about 60 angstroms, perhapsoptimally between about 25 angstroms and about 45 angstroms.

The optimal thickness range for a particular cover 90 may depend uponthe type of substrate to which the cover 90 is applied and upon theproduction procedures for such substrate. For example, glass sheets arecommonly tempered during production. Tempering may be performed toincrease the mechanical hardness of glass or to create internal stressesin glass that will cause such glass to shatter into many tiny pieceswhen broken, rather than breaking into large, dangerous shards. Duringtempering, glass is subjected to elevated temperatures before beingcooled at a controlled rate. For example, tempered glass is commonlyheated to temperatures at or near the melting point of glass. Morespecifically, tempering temperatures on the order of 600 degrees C. arecommon. Moreover, glass may be subjected to these high temperatures forextended periods of time (e.g., hours).

Unfortunately, the existing protective coatings discussed above (e.g.,papers, plastics, polymers, and the like) would not be expected tosurvive the elevated temperatures associated with glass tempering. Forexample, the above-noted Medwick et al. reference discloses a sputteredcarbon-containing coating that is expressly stated to be burned-offduring tempering. To the contrary, protective covers 90 of the presentinvention have been found to endure glass tempering quite well. In fact,the present covers 90 are believed to be ideal for use on glass that istempered (or otherwise heat-treated) after it has been coated. It hasbeen discovered though, that certain protective covers 90 havingthicknesses of less than about 20 angstroms can be negatively impactedby glass tempering procedures. As described below, these covers appearto become less protective than is desired after being subjected to glasstempering procedures. While this phenomenon does not appear to have beensatisfactorily explained, it is surmised to be a result of the cover 90material recrystallizing and changing in density during the temperingprocess. Thus, the present covers 90 desirably have thicknesses of atleast about 20 angstroms, more preferably at least about 25 angstroms,when such covers 90 are destined to be tempered or otherwiseheat-treated. It is anticipated, though, that the present covers 90would be quite effective in protecting non-temperable substrates atthicknesses as small as several angstroms.

The temporary protective cover 90 may comprise a film of any suitablematerial having the desired characteristics. As just described, it isadvantageous to form the protective cover 90 of material that is durableto elevated temperatures (e.g., glass tempering temperatures) on theorder of about 600 degrees C. In one embodiment, the cover material isone that is stable in the presence of water having a neutral pH, butbreaks down, dissolves, softens, or otherwise deteriorates in thepresence of a washing fluid that is at least slightly acidic or slightlybasic. For example, the cover 90 may be formed of material that breaksdown in the presence of a mild acid or a mild base. In a preferredembodiment, the cover 90 is formed of material that breaks down in thepresence of a weak organic acid, such as common household vinegar. Whilethe acidity of different vinegars may vary, the pH of common householdvinegar is estimated to be about 3. Alternatively, the temporary cover90 can be formed of material that breaks down in the presence of a weakbase, such as a weak ammonia solution. For example, in one suchembodiment, the cover 90 comprises a material that breaks down in thepresence of a common household ammonia solution, which is estimated tohave a pH of between about 11 and about 12.5.

The present temporary covers 90 can be formed of material that breaksdown in the presence of any desired washing fluid, whether or not suchwashing fluid is at all acidic or basic. Of course, the hydrophiliccoating 20 beneath the cover 90 is preferably formed of material that isdurable to the desired washing fluid. Since it is preferable in mostcases to form the protective cover 90 of material that is durable toindustrial glass washing processes, the desired washing fluid willtypically be one that is at least slightly acidic or basic.

Thus, the composition of the protective cover 90 is preferably selectedso as to complement the composition of the hydrophilic coating 20 thatwill carry the cover 90. In more detail, it is preferable to form theprotective cover 90 of material that will break down in the presence ofa selected washing fluid, which washing fluid conjointly will not breakdown or otherwise adversely affect the underlying hydrophilic coating20. For example, the cover 90 is preferably formed of material that canbe completely and uniformly removed when washed with the selectedwashing fluid. Furthermore, the hydrophilic coating 20 that carries theprotective cover 90 and is ultimately exposed upon removing the cover 90is preferably durable to (i.e., it does not substantially break down,dissolve, soften, or otherwise deteriorate in the presence of) theselected washing fluid. Thus, the material of the cover 90 isadvantageously selected to complement the nature of the hydrophiliccoating 20 it is intended to temporarily protect: the cover 90 is formedof material selected to break down when contacted by a washing fluid towhich the hydrophilic coating 20 is durable.

As noted above, when the cover 90 is carried by a sheet of glass, thecover 90 is advantageously formed of material that will withstand therigors of conventional glass production. In such embodiments, the cover90 is preferably stable in the presence of hot water and conventionalglass detergents, such as may be present in industrial glass washingmachines.

In certain embodiments, it may be advantageous to form the temporarycover 90 of an inorganic material. For example, this may be preferred incases where the underlying hydrophilic coating 20 also has aphotocatalytic effect. When the cover 90 is carried by a coating that isphotocatalytic, the cover 90 may deteriorate as a result of thedecomposition ability of the coating. Inorganic materials are generallythought to be durable to photoactivity. Thus, when a protective cover 90is carried on a photocatalytic coating, it is particularly preferred toform the cover 90 of an inorganic material.

In one embodiment of the invention, the temporary protective cover 90comprises an oxide of a metal. The term “metal” is used herein to referto metals and metalloids or semi-metals. Metal oxides tend to beadvantageous for a number of reasons. For example, the carbon-containingcoating of the above-noted Medwick et al. reference reportedly may drawoxygen out of a functional layer, to the extent such layer containsoxygen, upon which the carbon-containing coating may be deposited. Tothe contrary, one would not expect such a phenomenon to occur when usinga protective cover 90 that is a metal oxide, since a metal oxide is bydefinition already oxidized. Metal oxides also tend to have the desiredlevel of durability. Further, metal oxides can typically be depositedusing a variety of deposition techniques. In a particularly preferredembodiment, the present cover 90 comprises one or more of a number ofpreferred metal oxides. These preferred metal oxides include oxides ofmetals selected from the group consisting of zinc, bismuth, cadmium,iron, and nickel. The oxides of this group are stable in water, but tendto break down in the presence of weak acids or weak bases. Thus, theyare readily removed when washed with washing fluids that are mildlyacidic or mildly basic. They are also believed to be adequatelyprotective at the desired thickness ranges described herein.

It has been discovered that zinc oxide is markedly well suited for useas a temporary protective cover 90. Zinc oxide is especially preferredfor a number of reasons. For example, it has been found that zinc oxideis effective in protecting the hydrophilic coating 20 against surfacecontamination at a thickness of less than about 100 angstroms. In fact,protective covers 90 formed of zinc oxide have been found to beeffective in protecting the hydrophilic coating against surfacecontamination at thicknesses of about 20 angstroms or less, althoughthicknesses of at least about 25 angstroms are preferred when the cover90 is destined to undergo glass tempering. Further, it has beendiscovered that zinc oxide is particularly easy to remove in a completeand uniform manner when washed with a weak acid or a weak base (e.g.,vinegar). Zinc oxide can also be sputtered at a very high rate and isconsequently deposited at relatively low cost.

In one preferred embodiment, the temporary cover 90 comprises asputtered zinc oxide film having a thickness of at least about 25angstroms, more preferably between about 25 angstroms and about 60angstroms, and perhaps optimally between about 25 angstroms and about 45angstroms. As is described below, sputtered zinc oxide covers 90 in thisthickness range have been found to be particularly effective inprotecting substrate surfaces against contamination (e.g., when exposedto silicone), while being reliably removable in a complete, uniformmanner upon the application of a weak acid or a weak base. Moreover,such zinc oxide covers tend to be durable to glass tempering procedures.

Thus, the temporary cover 90 of the present invention desirably hasseveral characteristics. First, when applied to the hydrophilic coating20 at an easily removable thickness, it has the capacity to protect thecoating 20 from contamination, such as by silicone vapor or residue.Second, at the thickness used, the temporary cover is capable of beingbroken down and removed from the hydrophilic coating 20 with some easeby being washed with the desired washing fluid (e.g., an aqueoussolution that is at least slightly basic or slightly acidic). By “brokendown” or “breaks down” as used herein, we mean that the temporary cover90 is actually removed during the washing step. It is not removed in themanner that a protective polymer film might be mechanically peeled (orpulled) from the coating 20 that is to be protected. Rather, thetemporary cover 90 is capable of being dissolved in the desired washingfluid, or at least being softened or swollen in the washing fluid sothat it tends to disintegrate during the washing process. Preferably,substantially the entire cover 90 is removed during washing. Ideally,the cover 90 is capable of being removed completely from the hydrophiliccoating 20 during washing. Further, the composition of the protectivecover 90 is such that when it is removed by washing from the hydrophiliccoating 20, the washing step does not significantly affect theproperties of the hydrophilic coating 20. Accordingly, the hydrophiliccoating 20 is preferably impervious to the washing step that is requiredto remove the protective cover 90.

In a preferred embodiment of the invention, the protective cover 90comprises a film of sputtered material. Sputtered protective covers 90offer a number of advantages. For example, they are deposited within acontrolled sputtering environment. Thus, they provide protection againstcontamination as soon as the covered substrate is removed from thesputtering chamber. Further, the thickness of a sputtered protectivecover 90 can be controlled with a great deal of accuracy and uniformity,thus assuring that the substrate will be uniformly protected. Similarly,protective covers 90 that are substantially non-porous, and henceprovide desirable protection against contamination, can be readilyformed by sputtering. Surprisingly, it has been discovered thatsputtered covers 90 provide effective protection against surfacecontamination at thicknesses on the order of 10 angstroms. As notedabove, though, tempered substrates are preferably be provided withslightly thicker covers 90 (e.g., at least about 25 angstroms).

As noted above, the cover 90 can be advantageously formed of a sputteredmetal oxide film. A sputtered metal oxide film can be deposited usingvarious sputter deposition processes. One possibility for depositingsuch a film would be to sputter a target formed of the desired metaloxide itself in a non-reactive atmosphere, such as argon. However,targets formed of metal oxide tend not to sputter as reliably as puremetal targets, since metal oxides are less conductive than theirrespective metals. Thus, it can be difficult to reliably sputter a metaloxide target in a DC sputtering apparatus. As a consequence, metal oxidefilms are more commonly deposited by sputtering a metallic target in anoxidizing atmosphere. For example, a protective film 90 of zinc oxidecan be deposited by sputtering a zinc target in an oxidizing atmosphere(e.g., oxygen at a pressure of about 8×10⁻³ mbar).

Thus, in a particularly preferred embodiment, the protective cover 90 isformed by sputtering a metallic target in an oxidizing atmosphere. Aswill be readily appreciated by those skilled in the present art, thesputtering atmosphere can be varied to achieve the desired sputteringrate. For example, while the sputtering atmosphere may consist of pureoxygen, this is certainly not a requirement. In fact, a mixture ofoxygen and inert gas may enhance the sputtering rate. Thus, it isbelieved to be advantageous to employ a sputtering atmosphere comprisingoxygen and up to about 40% argon (preferably between 0-20%). As will bereadily appreciated by the those skilled in the art, the power appliedto the sputtering target can be varied to control the sputtering rateand reduce arcing.

One manufacturing arrangement that has given good results utilizes asingle planar target formed of metallic zinc. The target is sputtered ata power level of about 12 kW in a sputtering atmosphere comprising 100%O₂. The glass is moved past the sputtering target at a rate of about 300inches per minute.

FIG. 2 illustrates another embodiment of the present invention, whereina substrate 10 is provided with both a hydrophilic coating 20 and atemporary protective cover 90 on one side 12, and a reflective coating30 on the other 14. As those skilled in the present art will appreciate,this reflective coating 30 can take any desired form depending on theintended properties. For example, if the coated article is to be used asa mirror, then the reflective coating 30 may simply comprise one or morerelatively thick layers of a reflective metal. A wide variety ofreflective films are known in the art and the precise nature of suchreflective coatings is beyond the scope of the present invention.

The embodiment illustrated in FIG. 2 provides a particularly usefulreflective coating 30 that may be typified as an infrared-reflectivecoating (e.g., of the type commonly used as a low-emissivity coating).Typically, these coatings comprise a metal layer sandwiched between apair of dielectric (e.g., metal oxide or metal nitride) layers. Thisstructure can be repeated to further enhance the infrared reflectiveproperties of the film stack. One example of a useful infraredreflective film stack is disclosed in U.S. Pat. No. 5,302,449, issued toEby et al., the entire teachings of which are incorporated herein byreference.

The reflective coating 30 illustrated in FIG. 2 includes a base coat 32which may comprise one or more layers of dielectric materials. Forexample, this base coat 32 may comprise zinc oxide applied at athickness of between about 150 angstroms and about 275 angstroms. Afirst metal layer 34 can be applied directly on top of this base coat32. This metal can be, for example, silver applied at a thickness ofbetween about 100 angstroms and about 150 angstroms. A second dielectriclayer 38 can be applied over the first metal layer 34. The thickness ofthis dielectric layer 38 will depend, at least in part, on whether asecond metal layer 40 will be included in the film stack. In a filmstack having two metal layers, as shown, this second dielectric layer 38may typically comprise a relatively thick layer of a metal oxide, suchas 700-750 angstroms of zinc oxide. Preferably, a relatively thinprotective layer 36 is applied between the metal layer 34 and thedielectric layer 38. This will help protect the metal layer 34 duringsputter deposition of the dielectric layer 38. The protective layer 36may, for example, comprise a layer of metallic titanium or niobiumapplied at a thickness of 25 angstroms or less.

In the embodiment of FIG. 2, a second metal layer 40 is applied over thesecond dielectric layer 38. The second metal layer 40 will usually bemade of the same material as is the first metal layer 34. For example,this second metal layer 40 may comprise between about 125 angstroms andabout 175 angstroms of silver. A second protective layer 42 of titanium,niobium, or the like having a thickness of less than about 25 angstromsis preferably applied over this metal layer 40. As noted above, thislayer 42 is provided to protect the metal layer during subsequentdeposition of the overlying dielectrics 44 and 46. A third dielectriclayer 44 is applied over the protective layer 42. This dielectric layer44 can also be metal oxide or metal nitride, e.g., zinc oxide having athickness of between about 250 angstroms and about 300 angstroms. If sodesired, an protective outer layer 46 of a protective (i.e.,mechanically and/or chemically durable) material can be applied overthis dielectric layer 44. In one preferred embodiment, this layer 46comprises a film of Si₃N₄ having a thickness of between about 50angstroms and about 60 angstroms.

The reflective coating 30 on the interior surface 14 of the substrate 10illustrated in FIG. 2 does not carry a protective cover 90. If sodesired, however, a protective cover 90 can be applied over thisreflective coating 30. Thus, a further embodiment of the invention (notshown) involves a substrate 10, such as that illustrated in FIG. 2,which carries a protective cover 90 over the reflective coating 30 onthe interior surface 14 of the substrate 10.

A substrate like that shown in FIG. 2 is well suited for use inlow-emissivity articles. For example, a substrate of this nature iscommonly incorporated into a multiple-pane insulating glass unit (i.e.,an IG unit). IG units are well known in the present art and need not bediscussed in great detail. Briefly, though, an IG unit generallycomprises two or more panes (e.g., of glass) held in a spaced-apartrelationship by a spacer. The spacer 101 is typically formed of a hollowtube of metal or plastic. The spacer 101 can optionally be provided witha desiccant 103 that is allowed to communicate with the gas in thebetween-pane space 115. Such desiccant is useful in removing moisturethat may permeate between the panes. An edge seal 105 can be appliedaround the external periphery of the spacer to form a gas and moisturebarrier. For example, the edge seal 105 commonly comprises siliconewhich, as noted above, can outgas for extended periods of time. It canthus be appreciated that the presence of these edge seals 105 canpresent a very intimate contamination source for the panes 10, 100 of aninsulating glass unit.

FIG. 3 illustrates an IG unit wherein the confronting interior surfaces14, 114 of two spaced-apart panes 10, 100 bound between them a sealablebetween-pane space 115. As is common with low-emissivity insulatingglass units, one of the protected interior surfaces bears an infraredreflective coating 30. In the illustrated embodiment, the reflectivecoating 30 is borne on the interior surface 14 of the external pane 10.In the embodiment of FIG. 3, the exterior surface 12 of the externalpane 10 bears a hydrophilic coating 20 carrying a temporary protectivecover 90. While only one 12 of the exterior surfaces 12, 112 of theillustrated IG unit bears a hydrophilic coating 20 and a protectivecover 90 both of these surfaces 12, 112 could be provided with ahydrophilic coating 20 and/or a protective cover 90, if so desired. Forexample, it may be desirable to provide the exterior surface 112 of theinternal pane 100 with a protective cover 90 even if such surface 112 isnot provided with a hydrophilic coating.

If so desired, both sides of a substrate 10 like that shown in FIG. 1can be provided with a hydrophilic coating 20. For example, FIG. 4illustrates an embodiment of this nature wherein there is provided asubstrate 10 having a first hydrophilic coating 20 on its exteriorsurface 12 and a second hydrophilic coating 20 on its interior surface14. This would be particularly desirable where both surfaces 12, 14 ofthe substrate 10 are destined for exposure to periodic contact withwater. For example, this would be the case where both surfaces will beexposed to an outdoor environment.

In the embodiment of FIG. 4, each of the two hydrophilic coatings 20 onthe substrate 10 carries a temporary protective cover 90. Thus, ifeither covered surface were to become contaminated, then thecontaminated cover 90 could be readily removed to reveal the pristinesurface of the underlying hydrophilic coating 20. If so desired,however, one of the protective covers 90 on the illustrated substrate 10can be omitted. In such an embodiment (not shown), only one of thehydrophilic coatings 20 would be provided with a protective cover 90.

In the embodiment of FIG. 1, the substrate 10 bears a hydrophiliccoating 20 directly upon its exterior surface 12. As noted above,however, this is not a requirement. For example, the hydrophilic coating20 can alternatively be deposited over one or more films previouslydeposited on the exterior surface 12 of the substrate 10. Those skilledin the present art would be able to readily select the appropriate filmor films to impart desired properties in the substrate.

FIG. 5 illustrates one embodiment of this nature wherein a hydrophiliclayer 20 is deposited over a previously deposited low-emissivity layer80. The resulting coating 70 is referred to herein as a “hydrophiliclow-emissivity coating”. This coating 70 is also provided with aprotective cover 90. In the illustrated embodiment, the hydrophiliclow-emissivity coating 70 comprises a low-emissivity first layer 80formed directly upon the exterior surface 12 of the substrate 10, and ahydrophilic second layer 20 formed directly upon the low-emissivityfirst layer 80. As is thoroughly discussed in U.S. patent applicationSer. No. 09/868,543, the entire teachings of which are incorporatedherein by reference, a thus coated substrate can be used quiteadvantageous as a car windshield.

The low-emissivity first layer 80 desirably comprises apyrolytically-applied dielectric layer. This pyrolytic layer ispreferably applied directly upon the exterior surface 12 of thesubstrate 10. This pyrolytic layer can be formed of any desired materialthat yields a sufficiently durable coating with a commerciallyacceptable emissivity reduction as compared to plain, uncoated glass.The low-emissivity first layer 80 shown in the embodiment of FIG. 5 isformed by a single layer of material. It is to be understood, however,that this low-emissivity layer 80 can alternatively take the form of afilm stack having multiple individual layers. A variety of pyrolyticlow-emissivity coatings are well known in the art and a thoroughteaching of all pyrolytic coating techniques and compositions is beyondthe scope of the present disclosure.

A number of pyrolytically-applied coatings and techniques for theirdeposition have been well known in the art for a number of years and aredescribed in public literature. One suitable pyrolytically-appliedlow-emissivity film is a pyrolytic tin oxide that is commerciallyavailable under the trade name Energy Advantage from Libbey Owens Fordof Toledo, Ohio, U.S.A. While the exact coating in the Energy Advantageproduct is not fully known, it is believed that any of the widely-knowntechniques for pyrolytically applying tin oxide, for example, will yielda suitable layer.

A number of dopants are known in the art to enhance the conductivity,and hence improve the emissivity, of pyrolytically-applied layers suchas tin oxide. For example, fluorine may be the most common such dopant.One manner of applying a fluorine-doped pyrolytic tin oxide coating isdetailed in U.S. Pat. No. 5,698,262 (Soubeyrand et al.), the entireteachings of which are incorporated herein by reference. While thereader is referred to this patent for a highly detailed explanation ofsuch a coating, the disclosure of this patent is summarized brieflyherein. Generally, the tin oxide is applied by chemical vapor deposition(or “CVD”), wherein selected reactants are combined to form a uniform,vaporized reactant stream that is delivered to the surface of a hotglass substrate. The vaporized reactant stream reacts to deposit acoating of fluorine-doped tin oxide on the surface of the hot glasssubstrate. In the oxidizing atmosphere that exists at the surface of thehot glass, the organotin coating compounds pyrolytically decompose toform the tin oxide coating.

CVD pyrolytic deposition is typically conducted during the manufactureof glass by the float glass process, and occurs in a float metal bath, alehr, or in a transition zone between a bath and a lehr. The glasssubstrate is generally provided at a temperature in the range of betweenabout 7500° F. to about 15000° F. These are typical temperatures forglass during the various stages of manufacturing float glass.

The CVD reactant stream used by Soubeyrand et al. to deposit the tinoxide includes an organotin coating compound that is vaporized andconveyed to a point at or near the surface of the advancing glassribbon. Suitable organotin compounds are identified as includingdimethyltin dichloride, diethyltin dichloride, dibutyltin diacetate,tetramethyl tin, methyltin trichloride, triethytin chloride,trimethyltin chloride, ethyltin trichloride, propyltin trichloride,isopropyltin trichloride, sec-butyltin trichloride, t-butyltintrichloride, phenyltin trichloride, carbethoxyethyltin trichloride, andthe like, as well as combinations thereof. Soubeyrand et al. indicate apreference for dimethyltin dichloride. The organotin compound, andoptionally a carrier gas, oxidizer, stabilizer, hydrocarbon, inert gas,and the like are said to be vaporized to form a gaseous organotinreactant stream.

Soubeyrand et al. explain that the vaporized organotin compound can beprepared by any of the procedures set forth in U.S. Pat. Nos. 3,852,098;2,780,553; 4,351,861; 4,571,350; 3,970,037; 4,212,663; and 4,261,722,the entire teachings of each of which are incorporated herein byreference. Soubeyrand et al. state that they prefer to prepare thereactant stream containing the vaporized organotin compound byvaporizing the compound in a thin film evaporator in the presence of ablend gas, as is disclosed, for example, in U.S. Pat. No. 5,090,985, theentire teachings of which are also incorporated herein by reference.This gaseous stream, which generally comprises an inert carrier gas suchas helium, nitrogen, or argon, or mixtures thereof, can optionallycontain oxidizers such as water or oxygen. Preferred carrier gases aresaid to be helium and nitrogen, and mixtures thereof, containing oxygenas an oxidizer. The resultant reactant stream containing the vaporizedorganotin compound is generally heated to a temperature from about 250°F. to about 450° F., then conveyed to the reaction zone at the surfaceof the hot glass substrate.

Gaseous hydrogen fluoride or hydrofluoric acid (“HF” is used herein torefer to either hydrogen fluoride gas or hydrofluoric acid) is combinedwith the vaporized organotin compounds. Soubeyrand et al. create aseparate HF-containing reactant stream generally comprised of HF and acarrier, preferably water vapor. The addition of water to theHF-containing reactant stream is said to lower the emissivity of thecoated glass, while increasing the growth rate of the fluorine doped tinoxide deposited. The HF-containing reactant stream may additionallycontain conventional adjuvants such as for example helium, nitrogen, orargon, and mixtures thereof, as well as oxidizers such as for exampleoxygen.

The HF-containing reactant stream is combined with the organotinreactant stream at a point prior to delivery of the reactants to thesurface of the hot glass substrate upon which the coating is to bedeposited, but preferably in relatively close proximity thereto. Thereactant stream containing the HF can be prepared by vaporizing thecompound using one of the methods discussed hereinabove relative to thevaporization of the organotin, or by providing the HF as a gas. Thevaporized reactant stream containing the HF can be combined with thereactant stream containing the vaporized organotin compound by blendingthe two gaseous streams prior to delivery to the surface of the hotglass substrate. Alternatively, the HF-containing reactant stream inliquid or solution form can be injected into the hot reactant streamcontaining the vaporized organotin compound, thereby vaporizing thefluorine-containing solution or liquid compound. After combination, thevaporized reactants of organotin, HF, water and oxygen are delivered tothe surface of the hot glass, where they react together to depositthereon a coating of fluorine doped tin oxide.

Soubeyrand et al. teach exemplary gaseous reactant mixtures which aredelivered to the surface of the hot glass substrate as including (allpercentages being mole %) from about 10% to about 60% oxygen, from about2% to about 50% water, and from about 0.2% to about 2% HF, and mostpreferably includes from about 30% to about 50% oxygen, from about 15%to about 35% water, and from about 0.5% to about 1.5% HF. The uniform,gaseous reactant mixture also includes an organotin compound, thedesired concentration of which is a function of the desired thickness ofthe tin oxide coating and the line speed of the substrate. Thus,Soubeyrand et al. provide the organotin in the gaseous reactant mixturein an amount sufficient to apply a coating of the desired thickness atthe desired line speed of the substrate. For typical commercialoperations, the gaseous reactant mixture will generally include fromabout 0.01% to about 8% of the organotin.

Soubeyrand et al. also teach that it is desirable to apply a layer of amaterial that acts as a sodium diffusion barrier between the exteriorsurface of the sheet of glass and the fluorine-doped tin oxide coating.They found that coated glass articles exhibited lower emissivity, lowersheet resistance, and lower haze when the fluorine-doped tin oxidecoating was applied to the glass with a sodium diffusion layertherebetween, as opposed to directly on the glass. This sodium diffusionlayer is preferably formed of silicon dioxide. The layer of silicondioxide is preferably formed using conventional CVD techniques.

In Soubeyrand et al.'s preferred embodiment (which is incorporated asthe pyrolytic stack 25 shown in their FIG. 1), a thin film of tin oxideis first deposited on the exterior surface of the hot glass substrate,with a thin film of silicon dioxide deposited thereover, so that anunderlayer structure of tin oxide/silicon dioxide is formed intermediatethe glass and the subsequently deposited layer of fluorine-doped tinoxide. Soubeyrand et al. indicate that the silicon dioxide film not onlyacts as a sodium diffusion barrier but, in combination with the first(undoped) tin oxide film, helps to suppress iridescence in the resultingcoated glass article. The use of such “anti-iridescent” layers isdisclosed in U.S. Pat. No. 4,377,613, the entire teachings of which arealso incorporated herein by reference.

As illustrated in FIG. 5, the hydrophilic second layer 20 is desirably,though not necessarily, deposited directly upon the outer face of thelow-emissivity first layer 80. The hydrophilic second layer 20 maycomprise any suitable hydrophilic coating. As noted above, anexploration of all possible hydrophilic coatings is beyond the scope ofthe present disclosure. However, the preferred water-sheeting coatingdescribed above is expected to function particularly well in connectionwith pyrolytically-applied low-emissivity layers.

The hydrophilic coating 20 in the embodiment of FIG. 5 is desirablyapplied by sputtering, as described above. For example, the outer faceof the low-emissivity first layer 80 can be positioned beneath a silicontarget (optionally doped with aluminum) in an oxidizing sputteringatmosphere, and the target can be sputtered to deposit silicon dioxidedirectly upon the low-emissivity first layer 80. As noted above, theprecise operating conditions under which the hydrophilic coating 20 isapplied can be varied as necessary to control deposition of the coating20 at a desired thickness. The thickness of the hydrophilic coating 20can be on the same order as the hydrophilic coating 20 in the embodimentof FIG. 1. For example, a preferred thickness range is between about 15angstroms and about 350 angstroms, more preferably between about 15angstroms and about 150 angstroms, and perhaps optimally between about20 angstroms and about 120 angstroms. Given the present teaching as aguide, one of ordinary skill in the present art would be able to readilyselect and vary suitable operating conditions to deposit the hydrophiliccoating 20 at different thicknesses.

In the embodiment of FIG. 5, the interior surface 14 of the substrate 10does not carry a temporary protective cover 90. However, this interiorsurface 14 can be provided with a protective cover, if so desired. Thus,in a further embodiment (not shown), a substrate 10 like thatillustrated in FIG. 5 has a first cover 90 carried by the hydrophiliclow-emissivity coating 70 on its exterior surface 12, and a second cover90 on its uncoated interior surface 14.

Further, the interior surface 14 of the substrate 10 shown in FIG. 5 isuncoated. It may be desirable, however, to provide the interior surface14 of a substrate 10 of this nature with a hydrophilic coating 20. Theinterior surface 14 may alternatively, or additionally, be provided witha reflective coating 30, which can take any desired form depending onthe intended properties of the coated substrate. It can, for example, bean infrared-reflective coating 30 of the nature discussed above withreference to the embodiment of FIG. 2. Thus, in one embodiment (notshown) there is provided a substrate 10 having an exterior surface 12bearing a hydrophilic low-emissivity coating 70 that carries antemporary protective cover 90 while an interior surface 14 of thesubstrate 10 bears an infrared-reflective coating 30, optionallycarrying its own protective cover 90. A thus coated substrate wouldlikely provide particularly low emissivity, although visibletransmittance and reflectance may not be ideal for some applications.

The invention extends to a number of novel methods for producingsubstrates. For example, in one method of the invention, there isprovided a substrate having generally opposed interior 14 and exterior12 surfaces, which surfaces are typically major surfaces. A hydrophiliccoating 20 is formed upon the exterior surface 12 of the substrate 10.As noted above, the hydrophilic coating 20 preferably comprises materialthat is resistant to attack by a weak acid or a weak base. Thehydrophilic coating 20 may be formed directly upon the substrate,although this is certainly not required. In a particularly preferredembodiment, the hydrophilic coating 20 is formed by sputtering silicondioxide upon the substrate 10, as has been described. A temporaryprotective cover 90 can then be formed upon the hydrophilic coating 20.The cover 90 preferably comprises material that breaks down in thepresence of a weak acid or a weak base, as noted above. In oneembodiment, the cover 90 is formed of material that is durable toelevated temperatures on the order of 600 degrees C., and the methodfurther comprises tempering the covered substrate. In a preferredembodiment, the cover 90 is formed by sputtering upon the hydrophiliccoating 20 an oxide of a metal selected from the group consisting ofbismuth, cadmium, iron, nickel, and optimally zinc.

In another embodiment of the present invention, the method furthercomprises incorporating the covered substrate into an IG unit, asdescribed above. In still another embodiment, the method furthercomprises delivering the covered substrate to a customer. In yet anotherembodiment, the method further comprises installing the coveredsubstrate in a window frame, which may optionally then be installed inthe wall of a building.

The invention also extends to methods of processing substrates. Forexample, in one method there is provided a substrate having generallyopposed interior and exterior surfaces. The exterior surface bears ahydrophilic coating 20 that is durable to a given washing fluid. If sodesired, the washing fluid may be a mild acid or a mild base. Thehydrophilic coating 20 carries a temporary protective cover 90, whichmay advantageously comprise a sputtered film that protects thehydrophilic coating 20 against contamination, but that can be readilyremoved from the hydrophilic coating 20 by washing with the givenwashing fluid. As noted above, the selected washing fluid may be a mildacid or a mild base. The cover 90, for example, can be formed ofmaterial that is removable upon being washing with a household vinegar,such as would commonly have a pH of about 3. The protective cover 90 canbe removed from the hydrophilic coating 20 whenever it is desired toexpose this coating 20. The covered substrate can, for example, beprovided by a manufacturer of IG units or windows, by a distributor, bya home or building owner, or by a builder or contractor preparing toinstall the covered substrate in its final position (such as in a wallof a building).

The present method comprises washing the covered surface of thesubstrate with the given washing fluid to remove at least a portion ofthe cover 90, thereby exposing at least a portion of the hydrophiliccoating 20. Preferably, substantially the entire cover 90 is removed bythis washing. This washing step can be performed using any conventionalwashing technique. For example, the covered substrate surface can bewashed with a towel or the like moistened or soaked with the desiredwashing fluid (which may be a mildly acidic or mildly basic solution) inmuch the same way that the average homeowner cleans windows.Alternatively, it would likely be possible to remove the cover 90 bywashing the covered surface with a conventional squeegee device inconjunction with the desired washing fluid.

The washing step can be performed whenever it is desired to expose thehydrophilic coating 20. For example, it will generally be preferable notto remove the protective cover 90 until after the substrate has left themanufacturing facility, which is likely to be a contaminant-richenvironment. As noted above, the substrate may be exposed to a varietyof contamination sources even after leaving the manufacturingenvironment. For example, panes that are assembled into an IG unit aretypically exposed quite intimately to silicone sealants and the like,which are commonly applied during IG unit assembly. In such cases, thecover 90 can be advantageously left on the substrate 10 until thesubstrate 10 has been assembled into an IG unit or some other assembledproduct. In fact, it may be preferable to perform the washing step afterthe covered substrate has been delivered to an installation site or tothe ultimate consumer (e.g., a homeowner). In some cases, the washingstep may be performed following the installation of the coveredsubstrate in a position wherein the covered surface is oriented towardan outdoor environment. In such cases, the washing step will expose thehydrophilic coating 20 to periodic contact with water. It may be morepreferable not to perform the washing step until the covered substratehas been installed in its final position (e.g., in window frame whichmay optionally be mounted in the wall of a building). Perhaps optimally,the washing step is not performed until any finishing procedures (e.g.,painting a surrounding frame) have been completed on the substrate orits surroundings. By removing the protective cover 90 at such a latestage, the covered hydrophilic coating 20 can be protected againstcontamination during manufacturing, storage, transport, installation,and finishing. Thus, it is anticipated that it will be most preferred toperform the washing step, and thereby remove the cover 90, from thesubstrate 10 after all installation and finishing procedures have beencompleted.

As noted above, the temporary protective cover 90 is desirably appliedby sputtering. Likewise, the hydrophilic coating 20 and theinfrared-reflective coating 30, if either or both are present, arepreferably applied by sputtering. As described above, certainembodiments of the invention involve a substrate bearing coatings onboth major surfaces (i.e., on the interior and exterior surfaces). Inthese embodiments, both coatings (i.e., the interior and exteriorcoatings) can be deposited using conventional sputtering equipment byapplying these coatings in separate passes through a sputtering line.

In one method of the invention, before an infrared-reflective coating 30is sputtered onto the interior surface 14 of a substrate 10, ahydrophilic coating 20 and a protective cover 90 are sputtered onto theexterior surface 12 of the substrate 10. This can be accomplished bypositioning the exterior surface 12 of the substrate 10 beneath one ormore targets (e.g., silicon targets) adapted to sputter the desiredhydrophilic coating 20 material (e.g., silicon dioxide). The targets canthen be sputtered (e.g., in an oxidizing atmosphere) to deposit thehydrophilic coating 20 upon the exterior surface 12 of the substrate 10.Thereafter, the outer face of the hydrophilic coating 20 can bepositioned (e.g., conveyed to a subsequent sputtering chamber) beneathone or more targets (e.g., zinc targets) adapted to sputter the desiredprotective cover 90 material (e.g., zinc oxide). The targets can then besputtered (e.g., in an oxidizing atmosphere) to deposit the protectivecover 90 upon the outer face of the hydrophilic coating 20. Next, theinterior surface 14 of the substrate 10 can be positioned beneath one ormore targets adapted to sputter the film or films of theinfrared-reflective coating 30. These targets can then be sputtered todeposit the infrared-reflective coating 30 upon the interior surface 14of the substrate 10. Of course, the order of deposition can be reversed(i.e., the infrared-reflective coating 30 can be deposited on theinterior surface prior to depositing the hydrophilic coating and thecover on the exterior surface), if so desired.

FIG. 6 schematically illustrates a dual-direction sputtering chamber inaccordance with one embodiment of the present invention. As noted above,magnetron sputtering chambers are well known in the art and arecommercially available from a variety of sources. Thus, a detaileddiscussion of conventional magnetron sputtering chambers is beyond thescope of the present disclosure. In FIG. 6, the substrate 10 to becoated is positioned on a plurality of support rollers 210. The rollers210 are spaced along the length of the sputtering chamber 200. While theprecise spacing of these rollers 210 can be varied, for reasonsexplained more fully below, it may be desirable to space these rollers alittle bit farther apart, along at least a interim length of the chamber200, to increase the effective coating area from the lower target 260.

In the illustrated embodiment, the substrate 10 is oriented to travelhorizontally across the rollers, e.g., from left to right. The interiorsurface 14 of the substrate 10 is oriented upwardly, while the exteriorsurface 12 of the substrate is oriented downwardly to rest on (e.g., indirect supportive contact with) the rollers 210. While this is probablythe most typical configuration, it will be understood that the relativeorientation of the substrate 10 within the sputtering chamber 200 can beswitched, and the relative positions of the upper targets 200 and thelower target 260 also reversed. As a consequence, it should be notedthat designating these targets as “upper” and “lower” targets is simplyfor purposes of convenience and the relative orientation of theseelements within the sputtering chamber can easily be reversed if sodesired.

The sputtering chamber 200 shown in FIG. 6 includes two spaced-apartupper sputtering targets 220 a and 220 b. While these targets can beplanar targets, they are illustrated as being so-called rotary orcylindrical targets. These targets are arranged generally parallel toone another with a plurality of anodes 230 extending horizontally andgenerally parallel to these targets. As suggested in U.S. Pat. No.5,645,699 (Sieck), the entire teachings of which are incorporated hereinby reference, an intermediate anode 230 can also be positioned betweenthese two targets.

A gas distribution system is used to supply the sputtering gas to thechamber adjacent the targets 220 a and 220 b. While a variety of gasdistribution systems are known in the art, this distribution system maysimply comprise a pair of pipes 235 with a plurality of spaced-apartopenings or nozzles oriented generally toward the target.

The use of multiple targets positioned above a substrate in a magnetronsputtering chamber is fairly conventional in the field. The uniqueaspect of the sputtering chamber 200 in FIG. 6, though, is the presenceof the “lower” target 260. Lower targets can be used advantageously tosputter the hydrophilic coating 20 upon the exterior surface 12 of thesubstrate 10, and to subsequently sputter the protective cover 90 uponthe hydrophilic coating 20. As described below, upper targets can beused advantageously to deposit upon the interior surface 14 of thesubstrate 10 a film (e.g., a metal oxide) or films of theinfrared-reflective coating 30, if present.

While FIG. 6 illustrates a chamber 200 having only one lower target 260,the chamber 200 can be provided with two (or perhaps more) lowertargets, if so desired. As with the upper targets 220 a and 220 b, thelower target 260 is provided with at least one, and preferably two,anodes 270 in sufficient proximity to establish a stable plasma. The gasdistribution pipes 235 shown adjacent the upper targets 220 a and 220 bare undesirably far from the lower target 260 and the intermittentpresence of the substrate 10 will effectively divide the sputteringchamber 200 into two separate functional areas. Accordingly, it ispreferred to have separate gas distribution pipes 275 positioned beneaththe gas adjacent the lower target 260 to ensure a consistent supply ofgas for the plasma adjacent the lower target 260. If so desired, thelower pipes 275 and the upper pipes 235 may be a part of the same gasdistribution system, i.e., both sets of pipes can be connected to asingle gas supply.

The nature of the gas supplied by the upper 235 and lower 275 pipes willdepend at least in part on the composition of the upper 220 and lower260 sputtering targets. In conventional magnetron sputtering, the targetserves as a cathode. As noted above, it can be difficult to reliablysputter many commonly deposited materials, such as oxides of metals andsemi-metals, due to their electrically insulating nature. As a result,it is preferable in such cases to sputter targets comprising pure metalsand/or semi-metals. The material actually deposited can be oxidized byincluding oxygen in the gas supplied to the sputtering chamber.

While the substrate 10 will somewhat divide the sputtering chamber, thisdoes not preclude gas introduced in one area of the chamber fromtraveling elsewhere in the chamber. Accordingly, it is preferable thatthe gas supplied by the lower pipes 275 not adversely affect thesputtering of the upper targets 220 a and 220 b. Likewise, of course, itis preferable that the sputtering of lower target 260 not be adverselyaffected by the presence of the gas supplied through the upper pipes235. For example, use of this dual-direction sputtering chamber 200would not be as advantageous when depositing an oxide coating on oneside of the glass and an oxygen-sensitive metal on the other side.

More advantageously, a dual-direction sputtering chamber, such as thatillustrated in FIG. 6, can be used to deposit a first coating on theinterior surface 14 of the substrate 10 and a second coating on theexterior surface 12 of the substrate 10 in a single pass through thechamber. For example, the first and second hydrophilic coatings 20 on asubstrate 10 like that shown in FIG. 4 could be applied in a single passthrough such a dual-direction sputtering chamber 200. This could beaccomplished by utilizing upper 220 a and 220 b and lower 260 targetsformed of silicon, and sputtering these targets at substantially thesame time (e.g., simultaneously) in an oxidizing atmosphere. Adual-direction sputtering chamber 200 could also be used to deposit thefirst and second protective covers 90 upon a substrate 10 like thatshown in FIG. 4. This could be done by utilizing upper 220 and 220 b andlower 260 targets formed of zinc, and sputtering these targets atsubstantially the same time (e.g., simultaneously) in an oxidizingatmosphere. The oxidizing atmosphere in these methods can be establishedby introducing oxygen, or a mixture of oxygen and argon, through boththe upper pipes 235 and the lower pipes 275. In methods of this nature,any commingling of the gases introduced through the two sets of pipes235 and 275 should not adversely affect deposition of the interior orexterior coatings.

A dual-direction sputtering chamber 200 like that shown in FIG. 6 canalso be used to deposit interior and exterior coatings that differ incomposition. For example, a chamber of this nature could be used todeposit the hydrophilic coating 20 and one of the dielectric layers ofthe infrared-reflective coating 30 on a substrate 10 like that shown inFIG. 2. For example, this could be accomplished utilizing upper targets220 a and 220 b formed of a desired metal (e.g., zinc) and a lowertarget formed of silicon. These targets could then be sputtered atsubstantially the same time (e.g., simultaneously) in an oxidizingatmosphere. Thus, in a single pass through the chamber, a metal oxide(e.g., zinc oxide) of the infrared-reflective layer 30 could bedeposited on the interior surface 14 of the substrate 10 and thehydrophilic coating 20 (e.g., silicon dioxide) could be deposited on theexterior surface 12 of the substrate 10.

Alternatively, the protective cover 90 and one of the dielectric layersof the infrared-reflective coating 30 could be deposited upon asubstrate 10 like that shown in FIG. 2 in a single pass through adual-direction sputtering chamber 200. For example, this could beaccomplished utilizing upper 220 a and 220 b and lower targets formedrespectively of the desired metals (e.g., all targets could be zinc).These targets could then be sputtered at substantially the same time(e.g., simultaneously) in an oxidizing atmosphere. Thus, in a singlepass through the chamber, a metal oxide (e.g., zinc oxide) of theinfrared-reflective layer 30 could be deposited on the interior surface14 of the substrate 10 and a metal oxide (e.g., zinc oxide) protectivecover 90 could be deposited on the exterior surface 12 of the substrate10.

Even if one of the dielectric layers of the interior coating (e.g., aninfrared-reflective coating 30 ) comprises a nitride or the like, whilethe exterior coating (e.g., the hydrophilic coating 20 or the protectivecover 90 ) comprises a metal oxide in accordance with one embodiment ofthe invention, such materials can be simultaneously sputtered in thedual-direction chamber 200 so long as the introduction of some metaloxide into the nitride, and vice versa, being deposited will notadversely affect either of the coatings being applied. Ideally, though,the coating layer being deposited on the interior surface 14 is an oxide(or a partial oxide) when the hydrophilic coating 20 or protective cover90 deposited on the exterior surface 12 is a metal oxide. This assuresthat any commingling of the gases introduced through the two sets ofpipes 235 and 275 will not adversely affect the deposition of any ofthese coatings.

In conventional magnetron sputtering chambers, the spacing of therollers 210 used to support the substrate is kept fairly small to permitsmaller substrates to be processed on the line without any significantrisk of having the substrate fall between the rollers. In order tominimize the interference of the rollers in applying the coatings on theexterior surface 12 of the substrate, though, this spacing can beincreased.

The maximum safe spacing will need to be determined on a case-by-casebasis for a given range of anticipated substrate sizes. However, thelarger the spacing between the rollers disposed in the path from thelower target 260 to the exterior surface 12 of the substrate, thegreater the percentage of the sputtered material that will be depositedon the substrate. Of course, the rollers in other areas of thesputtering apparatus can be maintained at their normal spacing. It maybe desirable to make a few of the rollers in the dual-directionsputtering chamber 200 easily removed so the chamber can be convertedfrom the illustrated configuration to a more conventionally operatedchamber coating only one side of the substrate and having rollers spacedmore closely together. Instead of changing the spacing between therollers, the rollers could instead be made smaller in diameter. In orderto maintain the same transport speed of the substrate along the support,these smaller-diameter rollers could be turned more rapidly, e.g., bymeans of a pair of gears having the desired gear ratio.

The rollers 210 can be of any conventional structure. Conventionalrollers are hollow metal tubes. If so desired, the rollers can bestiffened, e.g., by filling them with a rigid foam. It has been foundthat good results can be obtained by employing cylindrical aluminumrollers about which a rope of Kevlar™ is spirally wound, with theKevlar™ providing the surface with which the substrate is in directcontact.

In some specific applications, the dual-direction sputtering chamber 200of FIG. 6 will be sufficient to entirely apply both of the desiredinterior and exterior coatings. More often, though, the sputteringchamber 200 would be part of a sputtering line comprising a series ofsputtering chambers. Each sputtering chamber in the line could includeboth an upper target and a lower target, but in most conventionalapplications, the film stack (e.g., an infrared-reflective film stack)applied to the upper surface of the substrate will be more complex(i.e., will comprise a series of distinct layers of varying composition)and thicker than the coating or coatings applied to the lower surface ofthe substrate. As a consequence, a majority of the chambers in asputtering line can comprise conventional, downward sputtering chambershaving only an upper target, with no target positioned beneath thesupports. If the sputtering line comprises a combination of downwardsputtering chambers and dual-direction sputtering chambers 200, theposition of the dual-direction chambers along the sputtering line can bevaried. For example, if a hydrophilic coating 20 or a protective cover90 comprising an oxide is applied by sputtering a lower target 260 in anoxidizing atmosphere, then one should not attempt to deposit anon-oxidized layer (e.g., an infrared-reflective silver layer such as isconventionally used in low-emissivity film stacks) onto the uppersurface of the glass in the same chamber. Accordingly, any chamber usedto sputter a pure metal layer is preferably operated as either adownward sputtering chamber or as an upward sputtering chamber, butpreferably not as a dual-direction sputtering chamber, by omitting thelower target.

A dual-direction sputtering chamber 200 such as that shown in FIG. 6 isbelieved to minimize the cost and maximize production efficiency inapplying coatings to both sides of a substrate. Less desirably, thecoatings on the interior side of the substrate (e.g., the low-emissivityfilm stack) can be applied in one pass, and the coatings on the exteriorside of the substrate (e.g., the hydrophilic coating and the protectivecover) can be applied in a second pass, flipping the glass between thepasses to permit all of the targets to be positioned on the same side ofthe supports in the sputtering chamber or line. However, this isbelieved to be much less efficient than the process outlined above, andis not as advantageous for low-cost commercial substrate production.

As the substrate moves through the chamber, there will be times when theglass does not effectively shield the upper targets 200 a and 200 b fromthe lower target 260 or vice versa. As a consequence, material from theupper targets will be deposited on the lower target and material fromthe lower target can be deposited on one or both of the upper targets.It is ideal to provide the sputtering chamber 200 of FIG. 6 with upper220 a, 220 b and lower 260 targets that have substantially the samecomposition. For example, the upper 220 a and 220 b and lower 260targets could all be zinc targets, such that with oxygen or a mixture ofoxygen and argon delivered through the upper 235 and lower 275 pipes, azinc oxide cover 90 can be applied on the exterior surface 12 of thesubstrate 10 at the same time that a zinc oxide dielectric layer of aninfrared-reflective coating 30 is deposited on the interior surface 14of the substrate 10. If the upper targets have a different compositionfrom the lower target, then cross-contamination of the different targetscould conceivably lead to problems in sputtering or in maintainingconsistent product quality.

At least in theory, this problem could be overcome by independentlycontrolling the power supplied to each of the sputtering targets toensure that each target is sputtering only when the substrate ispositioned to shield the upper and lower targets from one another.Current commercially available power supply controllers are notconfigured in this fashion, however. Furthermore, the control logic forsuch an arrangement can be unduly difficult if the sputtering line isused to coat substrates of varying sizes rather than a consistent size.

FIG. 7 illustrates one possible sputtering chamber 300 that can be usedto coat both the interior surface 14 and the exterior surface 12 of asubstrate 10 in a single pass without substantial cross contamination ofthe sputtering targets. Elements serving an analogous function toelements shown in FIG. 6 bear like reference numbers, but indexed by100, e.g., the upper gas distribution pipes 335 of FIG. 7 arefunctionally analogous to the upper gas distribution pipes 235 of FIG.6.

The sputtering chamber 300 of FIG. 7 is effectively divided into threecoating zones 300 a, 300 b and 300 c by a pair of barriers 340. Somefraction of the gas in one coating zone may flow into another coatingzone, so it is best to use a similar atmosphere in all three zones.However, the barriers 340 serve to effectively limit the amount ofmaterial sputtered in one coating zone which lands on a target inanother coating zone.

In the embodiment of FIG. 7, each of the three coating zones 300 a-300 cis adapted to hold up to four targets, with two targets positioned abovethe substrate and two positioned below the substrate. Hence, there aresix upper target mounts 321-326 positioned above the path of thesubstrate and six lower target mounts 361-366 positioned beneath thepath of the substrate. This allows maximum flexibility in using thissingle multi-zone sputtering chamber 300 to manufacture products havingdifferent properties. FIG. 7 schematically illustrates each of the uppertarget mounts 321-326 vertically aligned with one of the lower targetmounts 361-366, respectively. It should be understood, however, that thetargets need not be vertically aligned in this fashion and can be moreadvantageously positioned in a horizontally staggered arrangement.

In the configuration shown in FIG. 7, the first coating zone 300 a hastwo upper targets (320 a and 320 b), but no lower targets on the lowertarget mounts 361 or 362.

While a sputtering gas should be supplied to the upper gas distributionpipes 335 and power should be supplied to the upper anodes 330 in thefirst coating zone, there is no need to deliver any gas to the lower gasdistribution pipes 375 or any power to the lower anodes 370. The secondcoating zone 300 b has two lower targets 360 c and 360 d, but neither ofthe upper target mounts 323 and 324 carry sputtering targets. Similarly,the third coating zone 300 c has two lower targets 360 e and 360 f, butneither of the upper target mounts 325 and 326 carry sputtering targets.

The arrangement of targets in the multiple-zone sputtering chamber 300of FIG. 7 is merely illustrative and it will be understood that thetarget arrangement can be varied to maximize production efficiency fordifferent products. For example, if a thicker hydrophilic coating 20 isdesired at the same substrate speed, a silicon-containing target can bemounted on each of the lower target mounts 361-366 while none of theupper target mounts 321-326 can be provided with a target. If a thinnerhydrophilic coating 20 will suffice (or if substrate speed through thechamber is suitably reduced), then only the last two lower target mounts325 and 326 can be provided with targets while each of the first fourupper target mounts 321-324 carry sputtering targets. Of course, any oneor more of the coating zones 300 a-300 c can be operated much like thedual-direction sputtering chamber 200 of FIG. 6 by mounting targets inthe upper and lower target mounts of the same zone.

The equipment of FIGS. 6 and 7 and the methods of depositing coatingsusing such coating systems are discussed in the present applicationprimarily in the context of applying an infrared-reflective coating 30on one side of the substrate 10 and a hydrophilic coating 20 or aprotective cover 90 on the other side of the substrate 10. It is to beunderstood, however, that such equipment and methods can be used toapply coatings to both sides of a substrate regardless of the nature ofthe coatings applied thereto. For example, the apparatus can be used toapply a protective cover 90 on one side 14 of the substrate 10 and ahydrophilic coating 20 on the other side 12 of the substrate 10.

The advantage of the systems illustrated in FIGS. 6 and 7 is thatsputtered coating of the same or different composition can be applied toboth sides 12, 14 of a substrate 10 in a single pass through the coatingapparatus while the substrate 10 is maintained in a constantorientation, i.e. wherein it does not need to be flipped, turned orotherwise manipulated. This enables the use of a simple set of standardtransport rollers to move the substrate along the production line. Inthe absence of the present invention, one typically would have to eithermanually handle the substrate to flip it and send it back through thecoating apparatus in a separate run, or use a complex substrate handlingsystem which must hold the substrate and flip it at some point duringthe production process. This enables a substrate having coatings on bothsides to be produced particularly economically without any loss incoating quality.

In the past, it was assumed that even if one were to coat the bottomside of the substrate, contact with the rollers would mar that coatingor and/or damage the bottom surface of the substrate prior toapplication of the coating. Surprisingly, however, the present inventiondemonstrates that both sides of the substrate can be coated in a singlepass with excellent results.

The precise operating conditions (e.g. target composition, plasmacomposition, etc.) under which the various coatings of the invention areapplied can be varied as necessary to optimize the deposition of thedesired coating. Given the present teaching as a guide, one of ordinaryskill in the art should be able to select suitable operating conditionsto apply a given coating of the invention without undue experimentation.

The following non-limiting experimental examples illustrate theeffectiveness of the present temporary covers 90 in protectingsubstrates against contamination.

A comparative sample was prepared to provide an accurate comparison of ahydrophilic surface carrying a protective cover 90 of the invention to adirectly comparable hydrophilic surface without such a cover 90. In thefollowing Examples 1-3, two test samples, designated Sample A and SampleB, were provided. Sample A comprised a sheet of glass bearing ahydrophilic coating. Sample B comprised a sheet of glass bearing thehydrophilic coating of Sample A and carrying a protective cover 90 overthe hydrophilic coating.

The glass sheets of Sample A were produced in the following manner. Aclean surface of a sheet of soda-lime glass was sputter coated withsilicon dioxide in an oxidizing atmosphere comprising 80% oxygen and 20%argon. Three rotary targets each comprising about 95% silicon and about5% aluminum were operated at a power level of about 100 kW with theglass moving at a rate of about 300 inches per minute. The resultingsilicon dioxide coating had a thickness of about 53 angstroms.

The glass sheets of Sample B were produced in the following manner. Aclean surface of a sheet of soda-lime glass was sputter coated withsilicon dioxide in the same manner as in Sample A. Thereafter, atemporary protective cover 90 comprising zinc oxide was sputtered ontothe silicon dioxide coating. The zinc oxide was sputtered from a planarzinc target in an oxidizing atmosphere comprising 100% oxygen. Thetarget was operated at a power level of about 12 kW with the glassmoving at a rate of about 300 inches per minute. The resulting zincoxide covers had a thickness of about 16 angstroms.

EXAMPLE 1

Glass sheets of Sample A and Sample B were placed in a glass processingfacility adjacent barrels containing an uncured bulk silicone rubbermaterial. After about six hours of exposure to this environment, theglass sheets of both samples were tested for contamination.

Two different tests were performed to assess the extent to which thecoated glass surfaces had become contaminated. In the first test, thecontact angle of water on the coated glass surfaces was measured once ortwice using a commercially available measuring device. Hydrophilicsilicon dioxide coatings deposited under conditions such as those notedabove would be expected to have a contact angle with water of well below25° prior to any environmental exposure. Zinc oxide coatings depositedunder conditions such as those noted above would be expected to have acontact angle with water of below about 30° prior to any environmentalexposure.

In the second test, the ease of cleaning each sample was assayed byspraying a commercial glass cleaning liquid (Windex®) on the coatedsurface of each sample. That surface was then manually wiped with apaper towel until the surface appeared to be clean and essentiallystreak-free. The ease of cleaning (or “wipeability”) was assessed on ascale of 1-5, with the ease of cleaning normal uncoated glass (prior toany environmental exposure) being defined as 3, a very easy to cleanglass surface being rated 1, and a sample that is substantially moredifficult to clean being rated 5. While this rating system is somewhatsubjective, it does give a rough qualitative indication of the ease withwhich a glass surface can be cleaned.

The coated surfaces of both samples were then washed with a commonhousehold vinegar. This was done by scrubbing the samples with towelsmoistened in the vinegar in much the same way that one would ordinarilyclean a window. After the vinegar wash, the above tests were againperformed on both samples. The results of these tests were as follow:

TABLE 1 Contact Contact Angle Wipeability Angle Wipeability After AfterFollowing Following Vinegar Vinegar Sample Surface Exposure ExposureWash Wash A without 43° and 53° 3 23° 3 Cover B with 29° and 50° 2-310°-11° 1 Cover

Note that, following exposure to the contaminant, the coated surfaces ofboth samples exhibited greater contact angles than would be expected forsuch surfaces in an uncontaminated state. While the contact angles ofthe glass carrying a protective cover 90 of the invention (Sample B)were somewhat lower than those of the glass not carrying a cover 90(Sample A), neither of the samples exhibited particularly desirablecontact angles. Likewise, the wipeability ratings of both samplesindicate that, following exposure, neither Sample A nor Sample B wouldhave been particularly easy to clean in the proscribed manner.

After both samples were subjected to the vinegar wash, the silicondioxide coating that originally carried a protective cover 90 (Sample B)exhibited desirable hydrophilic surface properties that would beexpected for an uncontaminated silicon dioxide coating of this type. Thewipeability of this sample improved from a 2-3 rating to a much betterrating of 1, indicating that this sample had become very easy to clean.On the other hand, the vinegar wash had no apparent effect on thewipeability of the hydrophilic coating that was without a cover 90during exposure (Sample A), as the wipeability of this surface had amediocre rating of 3 before and after the vinegar wash. Moreover, thecontact angle of the sample that carried a cover 90 was reduced to10°-11°, which is less than half the final contact angle of the samplethat was without a protective cover 90.

These results indicate that the hydrophilic surface properties of adesirable silicon dioxide coating carrying a protective cover 90 of thepresent invention can be returned to a very desirable hydrophiliccondition, such as would be expected of an uncontaminated coating ofthis type, even after the covered surface has become contaminated withsilicone. Moreover, these results suggest that it is significantly lesseffective to attempt to wash this type of contamination from the silicondioxide coating in the proscribed manner once the coating has beendirectly exposed to silicone. Further, it is anticipated that washingwith any of a variety of liquids would not improve wipeability or reducecontact angles to the same extent as can be achieved with the presentcovers 90.

EXAMPLE 2

Glass sheets of Sample A and Sample B were placed in front of a largefan in a glass processing facility. After about six hours of exposure tothis environment, the glass sheets of both samples were tested forcontamination in the same manner as in Experimental Example 1. Theresults of these tests were as follow:

TABLE 2 Contact Contact Angle Wipeability Angle Wipeability After AfterSam- Following Following Vinegar Vinegar ple Surface Exposure ExposureWash Wash A without 40° and 43° 3-4 24° and 32° 3-4 Cover B with 35° and47° 3-4 15° and 14° 1 Cover

As was the case in Experimental Example 1, following exposure, bothsamples exhibited less desirable wipeability and contact angles thanwould be expected for uncontaminated surfaces of this nature.

After both samples were subjected to the vinegar wash, the silicondioxide coating that originally carried a protective cover 90 (Sample B)exhibited much better surface properties than the sample that waswithout a cover 90 (Sample A). The wipeability of this sample improvedsubstantially from a 3-4 rating to a very desirable rating of 1,indicating a very easy to clean surface. As was the case above, thevinegar wash had no apparent effect on the wipeability of the samplethat had been without a cover 90 (Sample A), as this sample had anunimproved wipeability rating of 3-4 even after the vinegar wash.Moreover, the contact angle of the sample that carried a cover 90 wasreduced to 15° and 14°, which is less than half that which was found onsome areas of the sample that was without a protective cover 90.

These results further support the effectiveness of the present covers 90in protecting hydrophilic surfaces against contamination. Moreover, theyindicate how surprisingly easily glass surfaces can become contaminated,as these samples were merely exposed to air blown by a fan in a typicalglass processing facility.

EXAMPLE 3

A deposit of silicone grease was applied to a central area of each glasssheet of Sample A and Sample B. After about six hours, the siliconegrease deposits were substantially removed by wiping the glass withclean paper towels. Both samples were then tested for contamination inthe same manner as in Examples 1 and 2. The results of these tests wereas follow:

TABLE 3 Contact Wipeability Angle Wipeability Contact After Sam-Following Following Angle After Vinegar ple Surface Exposure ExposureVinegar Wash Wash A without 27°-105° 2-3 23°-96° 1-3 Cover B with78°-105° 3 12° 1 Cover

Following this direct exposure to silicone grease, both samplesexhibited contact angles that were well beyond those which would beexpected for such surfaces in an uncontaminated state. The contactangles of both samples varied according to the particular areas of eachcoated surface on which measurements were taken. Higher contact angleswere typically found near the central areas of both sheets (i.e., wherethe silicone grease was deposited), while lower contact angles werecommonly found near the margins of the sheets (i.e., outside the area ofdirect application of the silicone). The contact angles in the centralareas of both samples were about 105 degrees, which indicates that theseareas had become badly contaminated. The wipeability ratings of bothsamples were also less than ideal, particularly in the central areas ofthe glass where the wipeability for both samples was a mediocre 3.

After both samples were subjected to the vinegar wash, the hydrophiliccoating that was protected by a cover 90 (Sample B) exhibited verydesirable surface properties. The wipeability of this sample improvedfrom an unimpressive rating of 3 to a much better rating of 1,indicating that this surface had become very easy to clean. Moreover,after the vinegar wash, the contact angle of this sample was reducedfrom a very hydrophobic 105 degrees in some areas to a desirablyhydrophilic 12 degrees across the entire surface.

On the other hand, the vinegar wash was less successful for thehydrophilic coating that was without a cover 90 (Sample A). Thewipeability of this sample had a rating of 2-3 before it was washed.While the vinegar wash did improve the wipeability of this sample insome areas, the central areas of the glass still exhibited a mediocrerating of 3. Similarly, while the contact angle range for this samplewas reduced slightly, the central areas of the glass still had contactangles of about 96 degrees, which is undesirably hydrophobic.

These results indicate that the present covers 90 are effective inprotecting glass surfaces against contamination even when a verydifficult-to-remove silicone contaminant is applied directly to thecovered glass.

EXAMPLE 4

An experimental sample, designated Sample C, comprising a sheet of glassbearing a hydrophilic coating was compared with another experimentalsample, designated Sample D, comprising a sheet of glass bearing thesame hydrophilic coating as in Sample C and carrying a protective cover90 over this hydrophilic coating.

The glass sheets of Sample C were produced in the following manner. Aclean surface of a sheet of soda-lime glass was sputter coated withsilicon dioxide in an oxidizing atmosphere comprising 80% oxygen and 20%argon. Three rotary targets comprising about 95% silicon and about 5%aluminum were operated at a power level of about 117 kW with the glassmoving at a rate of about 300 inches per minute. The resulting silicondioxide coating had a thickness of about 60 angstroms.

The glass sheets of Sample D were produced in the following manner. Aplain sheet of soda-lime glass was sputter coated with silicon dioxidein the same manner as in Sample C. Thereafter, a temporary protectivecover 90 of the invention comprising zinc oxide was sputtered onto thesilicon dioxide coating. The zinc oxide was sputtered in an oxidizingatmosphere comprising 100% oxygen. A planar zinc target was operated ata power level of about 13 kW with the glass moving at a rate of about300 inches per minute. The resulting zinc oxide covers had a thicknessof about 20 angstroms.

Prior to any environmental exposure, glass sheets of Sample C and SampleD were tested for wipeability and contact angle in the same manner as inExamples 1-3. The results of these tests were as follow:

TABLE 4A Sample Surface Contact Angle Wipeability C without Cover 18°1-2 D with Cover 17°-20° 1

A number of sealed insulating glass units were then assembled usingglass sheets of Sample C. Likewise, insulating glass units wereassembled using glass sheets of Sample D. A deposit of uncured siliconesealant was placed upon the pane of each unit opposite the pane bearingthe hydrophilic coating. The units were then stacked vertically on aconventional glass rack in a research laboratory for a period of days.

A first group of units, including Sample C units and Sample D units, wastested for contact angle and wipeability after a period of three days.The results of these tests were as follow:

TABLE 4B FIRST GROUP (UNITS EXPOSED FOR THREE DAYS) Contact WipeabilityAngle Wipeability Contact Angle After Sam- Following Following AfterVinegar Vinegar ple Surface Exposure Exposure Wash Wash C without 60° 452° 4 Cover D with 70° 4 10° 1 Cover

Following three days of exposure, the surface properties of both sampleswere substantially less desirable than they were prior to exposure. Thecontact angles of both samples were more than three times those of theglass prior to exposure. Moreover, the wipeability of Samples C and Dchanged from ratings of 1-2 and 1, respectively, to an undesirablerating of 4 for both samples.

After the vinegar wash, however, the surface properties of the glassthat originally carried a cover 90 were greatly improved. The contactangle of this sample (Sample D) dropped dramatically from 70 degrees to10 degrees. The wipeability of this sample also greatly improved from arating of 4 to a rating of 1, indicating that this sample had becomevery easy to clean.

The vinegar wash did not have the same effects on the surface propertiesof the sample that was without a cover 90 (Sample C). While the contactangle of this sample decreased slightly, it was still 52 degreesfollowing the vinegar wash, which would normally be higher than ispreferred for a hydrophilic coating. Furthermore, the vinegar wash hadno apparent effect on the wipeability of this sample, as it retained anundesirable rating of 4 even after washing.

A second group of units, including Sample C units and Sample D units,was tested for wipeability after a period of five days, while a thirdgroup was tested after 19 days. The results of these tests were asfollow:

TABLE 4C SECOND GROUP THIRD GROUP (UNITS EXPOSED FOR FIVE DAYS) (UNITSEXPOSED FOR 19 DAYS) Wipeability Wipeability Wipeability AfterWipeability After Following Vinegar Following Vinegar Sample SurfaceExposure Wash Sample Surface Exposure Wash C without 4 4 C without 4 4Cover Cover D with 2-3 1 D with 4 1 Cover Cover

Following both periods of exposure, the wipeability ratings of all ofthe samples were less desirable than they were prior to exposure,indicating that the samples had all become contaminated. After thevinegar wash, the wipeability of each sample that originally carried acover 90 was substantially improved. For example, the wipeability of thethird group of Sample D glass improved dramatically from a 4 rating to avery desirable rating of 1. Conversely, the vinegar wash had no apparenteffect on the wipeability of any of the samples that had been without acover 90.

These results indicate that the present covers 90 are effective inprotecting glass surfaces against contamination even throughoutprolonged periods of exposure. Further, the cumulative results ofExperimental Examples 1-4 indicate that the present protective covers 90are effective in protecting glass against contamination even atthicknesses on the order of 16-20 angstroms. As discussed below,however, it has been found that the present covers 90 desirably havethicknesses of at least about 25 angstroms when such covers 90 aredestined to be subjected to glass tempering.

EXAMPLE 5

To assess the effectiveness of the present covers 90 in protectingtempered glass against contamination at different thicknesses, thefollowing comparative samples were prepared.

TABLE 5A Sample Surface E 50 angstroms SiO₂, not carrying a cover F 50angstroms SiO₂, carrying cover having thickness of 10 angstroms G 50angstroms SiO₂, carrying cover having thickness of 20 angstroms H 50angstroms SiO₂, carrying cover having thickness of 30 angstroms I 50angstroms SiO₂, carrying cover having thickness of 40 angstroms J 35angstroms SiO₂, not carrying a cover K 35 angstroms SiO₂, carrying coverhaving thickness of 10 angstroms L 35 angstroms SiO₂, carrying coverhaving thickness of 20 angstroms M 35 angstroms SiO₂, carrying coverhaving thickness of 30 angstroms N 35 angstroms SiO₂, carrying coverhaving thickness of 40 angstroms

Sample E was produced in the following manner. A clean surface of asheet of soda-lime glass was sputter coated with silicon dioxide. Thesilicon dioxide was sputtered in an oxidizing atmosphere comprising 80%oxygen and 20% argon. Two rotary targets comprising about 95% siliconand about 5% aluminum were operated at a power level of about 27 kW withthe glass moving at a rate of about 260 inches per minute. The resultingsilicon dioxide coating had a thickness of about 50 angstroms.

Samples F-I were produced in the following manner. A clean surface of asheet of soda-lime glass was sputter coated with silicon dioxide in thesame manner as in Sample E. Thereafter, a temporary protective cover 90of the invention comprising zinc-tin oxide was sputtered onto thesilicon dioxide coating. The zinc-tin oxide was sputtered in anoxidizing atmosphere comprising 80% oxygen and 20% argon. The zinc-tinoxide covers of Samples F-I were deposited by operating a planarzinc-tin target (e.g., zinc and less than 15% tin) at power levels ofabout 6.8 kW, 13.7 kW, 20.5 kW, and 27.3 kW, respectively. The resultingzinc-tin oxide covers of samples F-I had thicknesses of about 10angstroms, 20 angstroms, 30 angstroms, and 40 angstroms, respectively.

Sample J was produced in much the same manner as Sample E. A cleansurface of a sheet of soda-lime glass was sputter coated with thesilicon dioxide. The silicon dioxide was sputtered in an oxidizingatmosphere comprising 80% oxygen and 20% argon. Two rotary targetscomprising about 95% silicon and about 5% aluminum were operated at apower level of about 27 kW with the glass moving at a rate of about 370inches per minute. The resulting silicon dioxide coating had a thicknessof about 35 angstroms.

Samples K-N were produced in the following manner. A clean surface of asheet of soda-lime glass was sputter coated with the silicon dioxidecoating of Sample J. A temporary protective cover 90 of the inventioncomprising zinc-tin oxide was then sputtered onto the silicon dioxidecoating. The zinc-tin oxide was sputtered from a planar zinc-tin target(e.g., zinc and less than 15% tin) in an oxidizing atmosphere comprising80% oxygen and 20 argon. The zinc-tin oxide covers of Samples K-N weredeposited by operating the target at power levels of about 9.7 kW, 20kW, 30 kW, and 40 kW, respectively. The resulting zinc-tin oxide coversof samples K-N had thicknesses of about 10 angstroms, 20 angstroms, 30angstroms, and 40 angstroms, respectively.

Glass sheets from all ten samples were then subjected to conventionalglass tempering temperatures (e.g., on the order of about 600° C.).Following tempering, each sample was measured for wipeability. A depositof uncured silicone sealant was then applied directly to a central areaof each glass sheet. The silicone deposits were left on the samples fora period of 3 days, after which the deposits were substantially removedby wiping the glass with towels. After this exposure, the wipeability ofeach sample was once again measured. Finally, a vinegar wash wasperformed on each sample whereafter the samples were once again testedfor the wipeability. The results of these measurements were as follow:

TABLE 5B Wipeability Wipeability Wipeability Sample Cover BeforeFollowing Following Vinegar ID Thickness Exposure Exposure Wash E nocover 1 4 3 F 10 angstroms 1 4 1 and 3 G 20 angstroms 1 4 1 and 3 H 30angstroms 1 4 1 I 40 angstroms 1 4 1 J no cover 1 4 4 K 10 angstroms 1 43-4 L 20 angstroms 1 4 2 M 30 angstroms 1 4 1 N 40 angstroms 1 4 1

Following exposure, the wipeability of all ten samples had decreasedfrom a rating of 1 to an undesirable rating of 4. As expected, thevinegar wash had little effect on the wipeability of the samples thatwere without a cover 90 (Samples E and J). Moreover, the vinegar washwas less effective on Samples F, G, K, and L. Each of these samplesoriginally carried a cover 90 with a thickness of either 10 or 20angstroms. For example, following the vinegar wash, Samples F and G wereleft with local surface areas that exhibited a mediocre wipeabilityrating of 3. Likewise, Sample K (10 angstrom cover) had an undesirable3-4 wipeability rating after the vinegar wash, while Sample L (20angstrom cover) was left with a wipeability rating of 2. In comparison,each of the samples with a 30 or 40 angstrom cover exhibited a uniformwipeability rating of 1 following the vinegar wash.

These results suggest that the 10 and 20 angstrom covers 90 werenegatively impacted by tempering. This may have been the result of theoxide cover recrystallizing, and perhaps changing in density andbecoming significantly porous. Thus, it is believed to be desirable toemploy a protective cover 90 having a thickness of at least about 25angstroms when the cover 90 is intended to endure glass temperingprocedures.

While a preferred embodiment of the present invention has beendescribed, it should be understood that various changes, adaptations andmodifications may be made therein without departing from the spirit ofthe invention and the scope of the appended claims.

1. An insulating glass unit comprising spaced-apart panes having confronting interior surfaces that bound a between-pane space, a desired one of the panes having an exterior surface bearing a hydrophilic coating that is durable to a given washing fluid, the hydrophilic coating carrying a temporary protective cover comprising a sputtered film that is durable to glass tempering and protects the hydrophilic coating against contamination but that can readily be removed from the hydrophilic coating by washing with said washing fluid, wherein the desired pane has an interior surface bearing a low-emissivity coating comprising a metal layer sandwiched between a pair of dielectric layers.
 2. The insulating glass unit of claim 1 wherein said panes have been tempered.
 3. The insulating glass unit of claim 1 wherein the hydrophilic coating has a contact angle with water of less than about 25 degrees when the cover is removed.
 4. The insulating glass unit of claim 1 wherein the sputtered film is stable in the presence of water.
 5. The insulating glass unit of claim 4 wherein said washing fluid is a mild acid or a mild base.
 6. The insulating glass unit of claim 5 wherein said washing fluid is vinegar.
 7. The insulating glass unit of claim 1 wherein the sputtered film comprises an oxide of a metal.
 8. The insulating glass unit of claim 7 wherein the sputtered film comprises an oxide of a metal selected from the group consisting of zinc, bismuth, cadmium, iron, and nickel.
 9. The insulating glass unit of claim 8 wherein the sputtered film comprises zinc oxide.
 10. The insulating glass unit of claim 1 wherein the sputtered film has a thickness of less than about 100 angstroms.
 11. The insulating glass unit of claim 10 wherein the sputtered film has a thickness of between about 25 angstroms and about 60 angstroms.
 12. The insulating glass unit of claim 1 wherein the sputtered film is formed directly upon the hydrophilic coating.
 13. The insulating glass unit of claim 12 wherein the hydrophilic coating is an oxide.
 14. An insulating glass unit comprising spaced-apart panes having confronting interior surfaces that bound a between-pane space, a desired one of the panes having an exterior surface bearing a hydrophilic coating, the hydrophilic coating canying a temporary protective cover comprising a sputtered film that is durable to glass tempering and protects the hydrophilic coating against contamination but that can readily be removed from the hydrophilic coating by washing with a weak acid or weak base, wherein the desired pane has an interior surface bearing a low-emissivity coating comprising a metal layer sandwiched between a pair of dielectric layers, wherein the sputtered film comprises an oxide of a metal selected from the group consisting of zinc, bismuth, cadmium, iron and nickel and has a thickness of between about 25 angstroms and about 60 angstroms, wherein the hydrophilic film comprises silicon dioxide and has a thickness of between about 15 angstroms and about 150 angstroms. 